Communication Method, Communications Apparatus, and Communications System

ABSTRACT

Embodiments of this application provide a communication method, a communications apparatus, and a communications system, to determine a physical resource block (PRB) grid when a center frequency of a synchronization signal (SS) is inconsistent with a center frequency of a carrier. The method includes: receiving, by a terminal, an SS from a network device; determining, by the terminal, a first PRB grid based on the SS; receiving, by the terminal, first indication information from the network device, where the first indication information is used to indicate a first frequency offset between the first PRB grid and a second PRB grid; and determining, by the terminal, the second PRB grid based on the first PRB grid and the first frequency offset.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2018/100072, filed on Aug. 10, 2018, which claims priority toChinese Patent Application No. 201710687875.7, filed on Aug. 11, 2017,and Chinese Patent Application No. 201710908898.6, filed on Sep. 29,2017. All of the aforementioned patent applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of this application relate to the field of communicationstechnologies, and in particular, to a communication method, acommunications apparatus, and a communications system.

BACKGROUND

In a wireless communications technology, after a terminal is powered on,the terminal accesses a wireless network after undergoing processes ofcell search, system information reception, and random access, to beserved by the wireless network. During the cell search process, theterminal detects a synchronization signal (SS), determines, based on theSS, a cell on which the terminal camps, and achieves downlinksynchronization with the cell.

The terminal detects the SS at a granularity of a channel raster. Thechannel raster is 100 kHz for all bands. In other words, a centerfrequency of a carrier is an integral multiple of 100 kHz. The SSincludes a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS). In frequency domain, the PSS and the SSSare mapped to six physical resource blocks (PRB) in the middle of thecarrier (namely, entire system bandwidth), namely, 72 subcarriers in themiddle of the carrier. Because the terminal does not yet achievedownlink synchronization with the cell in this case, to preventinterference, the PSS and the SSS are actually mapped to 62 subcarriersin the middle of the carrier, and five subcarriers on each side of the62 subcarriers play a protection function. It can be learned that the SSis located at a center of the carrier. In other words, a centerfrequency of the SS is consistent with (or the same as) the centerfrequency of the carrier. Therefore, after detecting the SS, theterminal can learn the center frequency of the carrier.

After the cell search, the terminal achieves downlink synchronizationwith the cell, and can receive downlink information that is sent by anetwork device through the cell. For example, the network devicebroadcasts bandwidth (or referred to as system bandwidth) information ofthe carrier on a physical broadcast channel (PBCH). The terminalreceives the bandwidth information of the carrier, and determinescarrier bandwidth based on the bandwidth information of the carrier. Inthis way, the terminal can obtain the center frequency of the carrierafter detecting the SS, obtain the carrier bandwidth after searching thePBCH, and then determine a grid of a physical resource block (PRB) ofthe carrier based on the center frequency of the carrier and the carrierbandwidth.

With development of communications technologies, the center frequency ofthe SS is no longer consistent with the center frequency of the carrier.The following problem may be caused if an existing manner of determininga PRB grid is used: Resources are misinterpreted and data cannot becorrectly received or transmitted, causing communication qualitydegradation.

SUMMARY

Embodiments of this application provide a communication method, acommunications apparatus, and a communications system, to determine aphysical resource block (PRB) grid when a center frequency of asynchronization signal (SS) is inconsistent with a center frequency of acarrier, so as to correctly receive or send data.

According to a first aspect, a communication method is provided. Themethod includes receiving, by a terminal, an SS from a network device.The method also includes determining, by the terminal, a first PRB gridbased on the SS. The method also includes receiving, by the terminal,first indication information from the network device, where the firstindication information is used to indicate a first frequency offsetbetween the first PRB grid and a second PRB grid. The method alsoincludes determining, by the terminal, the second PRB grid based on thefirst PRB grid and the first frequency offset.

According to a second aspect, a communication method is provided. Themethod includes sending, by a network device, an SS to a terminal basedon a first PRB grid. The method also includes sending, by the networkdevice, first indication information to the terminal, where the firstindication information is used to indicate a first frequency offsetbetween the first PRB grid and a second PRB grid. The method alsoincludes performing, by the network device, information transmissionwith the terminal based on the second PRB grid.

According to a third aspect, a communications apparatus is provided,where the communications apparatus is applied to a terminal, andincludes units or means configured to perform steps in the first aspect.

According to a fourth aspect, a communications apparatus is provided,where the communications apparatus is applied to a network device, andincludes units or means configured to perform steps in the secondaspect.

According to a fifth aspect, a communications apparatus is provided,including at least one processing element and at least one storageelement. The at least one storage element is configured to store aprogram and data. When the apparatus is applied to a terminal, the atleast one processing element is configured to perform the methodprovided in the first aspect of this application. When the apparatus isapplied to a network device, the at least one processing element isconfigured to perform the method provided in the second aspect of thisapplication.

According to a sixth aspect, a communications apparatus is provided,including at least one processing element (or chip) configured toperform the method according to the first aspect or the second aspect.

According to a seventh aspect, a program is provided, where when beingexecuted by a processor, the method according to the first aspect or thesecond aspect is performed.

According to an eighth aspect, a program product, for example a computerreadable storage medium, is provided, including the program according tothe seventh aspect.

According to the foregoing aspects, the network device indicates, to theterminal, a frequency offset between a PRB grid corresponding to an SSand a PRB grid corresponding to a data/control channel, so that whendetecting the SS, the terminal may determine, based on the PRB gridcorresponding to the SS and the frequency offset, the PRB gridcorresponding to the data/control channel. In this way, data/controlinformation can be correctly transmitted and received on thedata/control channel.

In an implementation, a subcarrier spacing of the second PRB grid is thesame as a subcarrier spacing of the SS.

In an implementation, the network device sends first indicationinformation through a physical broadcast channel (PBCH), and theterminal receives the first indication information through the PBCH.

In an implementation, the first indication information is used toindicate a frequency offset value, where an offset direction of thefirst PRB grid relative to the second PRB grid is predefined, or isindicated by using second indication information; or the firstindication information is used to indicate a frequency offset value, andan offset direction of the first PRB grid relative to the second PRBgrid.

In an implementation, there may be a plurality of subcarrier spacings,on a carrier, for data/control channel transmission. To determine PRBgrids corresponding to different subcarrier spacings, the foregoingmethod may further include: sending, by the network device, thirdindication information to the terminal, where the third indicationinformation is used to indicate a second frequency offset between thesecond PRB grid and a third PRB grid, and a subcarrier spacing of thethird PRB grid is greater than a subcarrier spacing of the SS; andreceiving, by the terminal, the third indication information, anddetermining the third PRB grid based on the second PRB grid and thesecond frequency offset.

In an implementation, the network device sends the third indicationinformation through the PBCH, or sends the third indication informationby using remaining minimum system information RMSI; or sends the thirdindication information by using a radio resource control (RRC) message.Correspondingly, the terminal receives the third indication informationthrough the PBCH, the RMSI, or the RRC message.

In this way, if the carrier supports a plurality of subcarrier spacings,when detecting the SS, the terminal may determine, based on the SS, aPRB grid used for the SS. When the subcarrier spacing of the SS is thesame as a subcarrier spacing of the data/control information, thenetwork device may determine, based on the first indication information,a PRB grid used for the data/control information; or when the subcarrierspacing of the SS is different from a subcarrier spacing of thedata/control information, the terminal may determine, based on thesecond indication information and a PRB grid corresponding to asubcarrier spacing that is the same as the subcarrier spacing of the SS,a PRB grid used for the data/control information. Therefore,data/control information can be correctly transmitted on a carrier thatsupports a plurality of subcarrier spacings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a communications system according to anembodiment of this application;

FIG. 2 is a schematic diagram of initially accessing a wireless networkby a terminal according to an embodiment of this application;

FIG. 3 is a frequency domain schematic diagram of an SS, a PBCH, and anSS block in which the SS and the PBCH are located according to anembodiment of this application;

FIG. 4 is a frequency domain schematic diagram of an SS according to anembodiment of this application;

FIG. 5 is a schematic diagram of an SS raster and a PRB grid accordingto an embodiment of this application;

FIG. 6 is a schematic diagram of a communication method according to anembodiment of this application;

FIG. 7 is a schematic diagram of a first PRB grid and a second PRB gridin a case according to an embodiment of this application;

FIG. 8 is a schematic diagram of a first PRB grid and a second PRB gridin another case according to an embodiment of this application;

FIG. 9 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 10 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 11 is a schematic diagram of PRB grids corresponding to a pluralityof subcarrier spacings according to an embodiment of this application;

FIG. 12 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 13 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 14 is a schematic diagram of a PRB grid according to an embodimentof this application;

FIG. 15 is a schematic diagram of initially accessing a network by aterminal according to an embodiment of this application;

FIG. 16 is a schematic diagram of transmitting different SSs on awideband carrier according to an embodiment of this application;

FIG. 17 is a schematic diagram of accessing a same carrier by differentterminals by using different SSs according to an embodiment of thisapplication;

FIG. 18 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 19 is a schematic diagram of accessing a same carrier by differentterminals by using different SSs according to an embodiment of thisapplication;

FIG. 20 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 21 is a schematic diagram of another communication method accordingto an embodiment of this application;

FIG. 22 is a schematic structural diagram of a network device accordingto an embodiment of this application;

FIG. 23 is a schematic structural diagram of a terminal according to anembodiment of this application;

FIG. 24 is a schematic diagram of still another communication methodaccording to an embodiment of this application;

FIG. 25 is a schematic diagram of a PRB grid according to an embodimentof this application; and

FIG. 26 is a schematic diagram of another PRB grid according to anembodiment of this application.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For ease of understanding by a person skilled in the art, the followingdescribes some terms in the embodiments of this application.

(1) A terminal, also referred to as user equipment (UE), a mobilestation (MS), a mobile terminal (MT), or the like, is a device thatprovides voice/data connectivity for a user, for example, a handhelddevice or an in-vehicle device having a wireless connection function.Currently, some examples of the terminal are: a mobile phone, a tabletcomputer, a notebook computer, a palmtop computer, a mobile Internetdevice (MID), a wearable device, a virtual reality (VR) device, anaugmented reality (AR) device, a wireless terminal in industrialcontrol, a wireless terminal in self driving, a wireless terminal in aremote medical surgery, a wireless terminal in a smart grid, a wirelessterminal in transportation safety, a wireless terminal in a smart city,a wireless terminal in a smart home, and the like.

(2) A network device is a device that provides a wireless service for aterminal, and includes, for example, a radio access network (RAN) node(or device). A RAN node (or device) is a node (or device), in a network,to connect a terminal to a wireless network. Currently, some examples ofthe RAN node are: a gNB, a transmission reception point (TRP), anevolved NodeB (eNB), a radio network controller (RNC), a NodeB (NB), abase station controller (BSC), a base transceiver station (BTS), a homebase station (for example, a home evolved NodeB or a home NodeB, HNB), abaseband unit (BBU), or a Wi-Fi access point (AP). In addition, in anetwork structure, a RAN includes a centralized unit (CU) node or adistributed unit (DU) node. In this structure, functional division on aRAN side is implemented in the CU and the DU, and a plurality of DUs arecentrally controlled by one CU. In this case, the RAN node may be a CUnode/a DU node. Functions of the CU and the DU may be divided based onprotocol layers of a wireless network. For example, functions of aPacket Data Convergence Protocol (PDCP) layer are arranged in the CU,and functions of protocol layers below the PDCP layer, for example, aRadio Link Control (RLC) layer and a Media Access Control (MAC) layer,are arranged in the DU. The division based on protocol layers is only anexample, and there may be other division based on protocol layers, forexample, division at the RLC layer, where functions of the RLC layer anda protocol layer above the RLC layer are arranged in the CU, andfunctions of a protocol layer below the RLC layer are arranged in theDU; or, division in a particular protocol layer, for example, somefunctions of the RLC layer and functions of a protocol layer above theRLC layer are arranged in the CU, and remaining functions of the RLClayer and functions of a protocol layer below the RLC layer are arrangedin the DU. In addition, there may be division in another manner, forexample, division based on a delay, to arrange a function that needs tomeet a delay requirement in the DU, and arrange a function that is lowerthan the delay requirement in the CU.

(3) “A plurality of” means two or more, and other quantifiers aresimilar. The character “/” describes an association relationship fordescribing associated objects and represents that three relationshipsmay exist. For example, A/B may represent the following three cases:Only A exists, both A and B exist, and only B exists.

FIG. 1 is a schematic diagram of a communications system according to anembodiment of this application. As shown in FIG. 1, a terminal 120accesses a wireless network through a network device 110, to be servedby an external network (for example, the Internet) through the wirelessnetwork or communicate with another terminal through the wirelessnetwork. After the terminal 120 is powered on, the terminal initiallyaccesses the wireless network to be served by the wireless network andto transmit and receive data. The following is described with referenceto FIG. 2. FIG. 2 is a schematic diagram of initially accessing awireless network by a terminal according to an embodiment of thisapplication. After the terminal is powered on, the terminal initiallyaccesses the wireless network after undergoing processes of cell search,system information reception, random access, and the like, and then canperform data transmission (TX) and reception (RX).

During the cell search, the terminal detects a synchronization signal(SS), determines, based on the SS, a cell on which the terminal camps,and achieves downlink synchronization with the cell. In a Long TermEvolution (LTE) communications system, the terminal detects the SS at agranularity of a channel raster. The channel raster is 100 kHz for allbands. In other words, a center frequency of a carrier is an integralmultiple of 100 kHz. The SS includes a primary synchronization signal(PSS) and a secondary synchronization signal (SSS). In frequency domain,the PSS and the SSS are mapped to six physical resource blocks (PRB) inthe middle of the carrier (namely, entire system bandwidth), namely, 72subcarriers in the middle of the carrier. Because the terminal does notyet achieve downlink synchronization with the cell in this case, toprevent interference, the PSS and the SSS are actually mapped to 62subcarriers in the middle of the carrier, and five subcarriers on eachside of the 62 subcarriers play a protection function. It can be learnedthat the SS is located at a center of the carrier. In other words, acenter frequency of the SS is consistent with (or the same as) thecenter frequency of the carrier. Therefore, after detecting the SS, theterminal can learn the center frequency of the carrier. After the cellsearch, the terminal achieves downlink synchronization with the cell,and can receive downlink information that is sent by a network devicethrough the cell. For example, the network device broadcasts bandwidth(or referred to as system bandwidth) information of the carrier on aphysical broadcast channel (PBCH). The terminal receives the bandwidthinformation of the carrier, and determines carrier bandwidth based onthe bandwidth information of the carrier. In this way, the terminal canobtain the center frequency of the carrier after detecting the SS,obtain the carrier bandwidth after searching the PBCH, and thendetermine a grid of a physical resource block (PRB) of the carrier basedon the center frequency of the carrier and the carrier bandwidth.

In a fifth generation (5G) mobile communications system, also referredto as a new radio (NR) communications system, a terminal initiallyaccesses a wireless network also after undergoing processes of cellsearch, system information reception, random access, and the like. Inthe NR communications system, a concept of a synchronization signalblock (SS block) is introduced. The SS block includes an SS and aphysical broadcast channel (PBCH), where the SS includes a PSS and anSSS. FIG. 3 is a frequency domain schematic diagram of an SS, a PBCH,and an SS block in which the SS and the PBCH are located according to anembodiment of this application. As shown in FIG. 3, the SS blockoccupies 24 PRBs in frequency domain, namely, 288 subcarriers. Centrallocations of the SS and the PBCH in frequency domain are a centrallocation of the SS block in frequency domain. In other words, centerfrequencies of the SS and PBCH are aligned with or consistent with acenter frequency of the SS block. The SS occupies 12 PRBs, namely, 144subcarriers; and the PBCH occupies 24 PRBs, namely, 288 subcarriers. Inother words, the SS is mapped to 12 PRBs, and the PBCH is mapped to 24PRBs.

FIG. 4 is a frequency domain schematic diagram of an SS according to anembodiment of this application. As shown in FIG. 4, the SS is mapped toa 7^(th) PRB to an 18^(th) PRB of an SS block, and the 12 PRBs include144 subcarriers numbered from 0 to 143, where an SS sequence is mappedto subcarriers numbered from 8 to 134. No data is mapped to first eightsubcarriers and last nine subcarriers, so as to play a protectionfunction.

A network device sends the SS block based on an SS raster. In otherwords, the SS can be sent only at a location of the SS raster, andinformation is sent on a PBCH. A terminal blindly detects the SS basedon the SS raster, that is, detects the SS at the location of the SSraster. After detecting the SS, the terminal can learn of a centerfrequency of the SS, and then receives the information on the PBCH on 24PRBs that center on the center frequency of the SS. The SS raster is araster formed at a possible location of the SS in frequency domain. Whenthe SS is sent at a location of the SS raster, the center frequency ofthe SS is at this location. Subsequently, when the network device noperiodically sends the SS in time domain, the location of the SS infrequency domain does not change. When detecting the SS, the terminalmay determine, based on the center frequency of the SS and a subcarrierspacing of the SS, a PRB grid corresponding to the SS, where thesubcarrier spacing of the SS is a subcarrier spacing used for SStransmission/reception. However, a PRB grid that is used when thenetwork device transmits data/control information centers on a centerfrequency of a carrier, and a size of the PRB grid is determined basedon a subcarrier spacing of the data/control information, where thesubcarrier spacing of the data/control information is a subcarrierspacing used for data/control information transmission/reception. If theterminal still performs the data/control informationtransmission/reception based on the PRB grid corresponding to the SS,because the PRB grid corresponding to the SS is probably inconsistentwith the PRB grid used by the network device, a PRB resource ismisinterpreted, and data cannot be correctly transmitted or received.

The foregoing problem is described below with reference to FIG. 5 byusing an example in which a channel raster is 100 kHz, an SS raster is180 kHz, and a subcarrier spacing of an SS is 15 kHz. FIG. 5 is aschematic diagram of an SS raster and a PRB grid according to anembodiment of this application. A distance between two adjacent verticallines at a lower part of FIG. 5 represents a size of the SS raster,namely, 180 kHz; and a distance between two adjacent vertical lines atan upper part of FIG. 5 represents a size of a channel raster, namely,100 kHz. Two middle PRB grids are respectively a PRB grid correspondingto a data/control channel on a carrier and a PRB grid corresponding toan SS. Herein, assuming that a subcarrier spacing of the data/controlchannel on the carrier is the same as a subcarrier spacing of the SS,sizes of the PRBs are the same. Assuming that a network device sends theSS at a location 510, the terminal performs blind detection based on theSS raster, and detects the SS at the location 510. It is assumed thatthe location 510 is 180*N kHz, where N is a non-negative integer. Acenter frequency of the carrier is located at a center of the carrier,and is an integral multiple of the channel raster. When a quantity ofPRBs of the carrier is an even number, the center frequency of thecarrier is located between two PRBs, namely, at an intersection of thetwo PRBs. When the quantity of PRBs of the carrier is an odd number, thecenter frequency of the carrier is located at a center of anintermediate PRB. Assuming that the center frequency of the carrier is100*M kHz, an offset value between the center frequency of the carrierand the location 510 is |180*N kHz−100*M kHz|, where “∥” indicatesacquisition of an absolute value. If the subcarrier spacing of the SS is15 kHz, a size of a PRB corresponding to the SS is 15*12 kHz, namely,180 kHz; and a size of a PRB corresponding to the data/control channelis also 180 kHz. In this case, the PRB grid corresponding to the SS maynot be aligned with the PRB grid corresponding to the data/controlchannel. If the terminal receives or transmits data based on the PRBgrid corresponding to the SS, there may be a problem that a resource ismisinterpreted and data cannot be correctly received or transmitted,causing communication quality degradation.

In consideration of the foregoing problem, the following embodimentsprovide several solutions, so as to address an issue in determining aPRB grid.

In a solution, the network device indicates, to the terminal, afrequency offset between the PRB grid corresponding to the SS and thePRB grid corresponding to the data/control channel. Therefore, whendetecting the SS, the terminal can determine, based on the PRB gridcorresponding to the SS and the frequency offset, the PRB gridcorresponding to the data/control channel. In this way, data/controlinformation can be correctly transmitted and received on thedata/control channel. In this solution, it is assumed that the PRBcorresponding to the SS and the PRB corresponding to the data/controlchannel have a same subcarrier spacing.

There may be a plurality of subcarrier spacings, on a carrier, fordata/control channel transmission. When a subcarrier spacing used fordata/control channel transmission is the same as the subcarrier spacingof the SS, it is assumed that a PRB grid used for the carrier in thiscase is a PRB grid G₁; or when a subcarrier spacing for data/controlchannel transmission is different from the subcarrier spacing of the SS,it is assumed that a PRB grid used for the carrier in this case is a PRBgrid G₂. The PRB grid G₁ may be obtained by using the foregoingsolution, to transmit and receive data/control information on thedata/control channel. When the subcarrier spacing used for thedata/control channel transmission is greater than the subcarrier spacingof the SS, the network device may indicate, to the terminal, a frequencyoffset between the PRB grid G₂ and the PRB grid G₁. Therefore, theterminal can obtain the PRB grid G₁ by using the foregoing method, andthen obtain the PRB grid G₂, to transmit and receive data/controlinformation on the data/control channel. Alternatively, the networkdevice may indicate, to the terminal, a frequency offset between aboundary of the PRB grid G₂ and the center frequency of the SS.Therefore, the terminal can determine the PRB grid G₂ based on thecenter frequency of the SS and the frequency offset, to transmit andreceive data/control information on the data/control channel. When thesubcarrier spacing used for the data/control channel transmission issmaller than the subcarrier spacing of the SS, because there is anesting relationship between PRB grids corresponding to differentsubcarrier spacings, the PRB grid G₂ may be directly obtained based onthe PRB grid G₁ and the subcarrier spacing used for the data/controlchannel transmission, to transmit and receive data/control informationon the data/control channel.

In the embodiments of this application, frequency offsets are absolutevalues, where a frequency offset between A and B may be an absolutevalue of a frequency offset of A relative to B, or may be an absolutevalue of a frequency offset of B relative to A. In addition, in theembodiments of this application, a PRB grid may be understood as a PRBgrid structure.

The following is described with reference to the accompanying drawings.

FIG. 6 is a schematic diagram of a communication method according to anembodiment of this application. As shown in FIG. 6, the method includesthe following steps:

S610. A network device sends an SS to a terminal.

S620. The terminal detects the SS.

S630. When the SS is detected, the terminal determines a first PRB grid(a PRB grid G₀) based on the SS. In other words, when receiving the SSfrom the network device, the terminal determines the first PRB grid (thePRB grid G₀) based on the SS.

The network device sends indication information I₁ to the terminal,where the indication information I₁ is used to indicate a frequencyoffset F₁ between the first PRB grid (the PRB grid G₀) and a second PRBgrid (a PRB grid G₁).

S650. The terminal determines the second PRB grid (the PRB grid G₁)based on the first PRB grid (the PRB grid G₀) and the frequency offsetF₁.

After the second PRB grid (the PRB grid G₁) is determined, if thenetwork device performs data/control information transmission on acarrier by using a subcarrier spacing that corresponds to the second PRBgrid (the PRB grid G₁), or the network device allocates a resource tothe terminal based on the second PRB grid (the PRB grid G₁), thedata/control information transmission may be performed between theterminal and the network device based on the second PRB grid (the PRBgrid G₁) (in S660).

The first PRB grid (the PRB grid G₀) may be referred to as a PRB grid (aPRB grid G₀) used for an SS (or an SS block), and the second PRB gridmay be referred to as a PRB grid (a PRB grid G₁) used for a carrier. Thefirst PRB grid is a PRB grid corresponding to a subcarrier spacing ofthe SS (or the SS block) in frequency domain. The second PRB grid may bea PRB grid corresponding to a subcarrier spacing of physical channelinformation/a physical signal on the carrier in frequency domain. Thephysical channel herein is a physical channel other than a PBCH. Forexample, the physical channel includes at least one of anuplink/downlink control channel, an uplink/downlink shared channel (alsoreferred to as a data channel), and a random access channel. Thephysical channel information is information carried on the physicalchannel. The physical signal is a physical signal other than an SS. Forexample, the physical signal includes a reference signal. In theforegoing description, a data/control channel is used as an example, anda random access channel or a physical signal is similar thereto.

In the foregoing step S610, the network device sends the SS at alocation of an SS raster, and a center frequency of the SS is located atthe location. However, the terminal does not know the location at whichthe network device sends the SS. Therefore, in the foregoing step S620,the terminal performs blind detection based on the SS raster. When theSS is detected at a first location of the SS raster, it may bedetermined that the location at which the network device sends the SS isthe first location, namely, the center frequency of the SS. In addition,the network device can simultaneously broadcast information on a PBCH inS610. When detecting the SS in S620, the terminal may determine thecenter frequency of the SS, and may also determine a center frequency ofthe PBCH that is consistent with the center frequency of the SS; andthen may determine a frequency domain location of the PBCH, therebyreceiving, on the PBCH, the information broadcast by the network device.

In the foregoing step S630, the terminal determines the first PRB gridbased on the first location of the SS raster (namely, the centerfrequency of the SS) and the subcarrier spacing of the SS. A boundary ofthe first PRB grid is located at the first location, and a size of a PRBin the first PRB grid is a product of the subcarrier spacing of the SSand a quantity (for example, 12) of subcarriers in the PRB. For example,as shown in FIG. 5, when the terminal detects the SS at a location 510,a boundary of the first PRB grid is located at the location 510. If asize of the subcarrier spacing of the SS is 15 kHz, the size of the PRBis 180 kHz. In this way, a PRB grid at a lower part of FIG. 5, namely,the first PRB grid, may be obtained.

In the foregoing step S640, the network device may send the indicationinformation I₁ to the terminal through the PBCH. For example, thenetwork device broadcasts a master information block (MIB) on the PBCH,where the MIB carries the indication information I₁. The terminaldetermines the frequency domain location of the PBCH, where the centerfrequency of the PBCH is the center frequency of the SS, and the PBCH ismapped to 24 PRBs on two sides of the center frequency; and receives, onthe PBCH, the indication information I₁ broadcast by the network device.The indication information I₁ may be the frequency offset F₁, or may beindication information of the frequency offset F₁. For example, theindication information I₁ may be 1-bit information. When the indicationinformation I₁ is “0”, it indicates that the frequency offset F₁ is 0.In other words, there is no frequency offset. The first PRB grid isaligned with the second PRB grid. In this case, when the first PRB gridis determined, the second PRB grid is determined. For another example,when the indication information I₁ is “1”, it indicates that thefrequency offset F₁ is half a PRB. In this case, in step S650, the firstPRB grid may be offset by half a PRB to obtain the second PRB grid.

In the foregoing step S650, the terminal moves the first PRB grid infrequency domain based on the frequency offset F₁ that is indicated inthe indication information I₁, to obtain the second PRB grid.

When the second PRB grid is obtained, data/control informationtransmission, including uplink transmission/downlink transmission, maybe performed between the terminal and the network device based on thesubcarrier spacing that corresponds to the second PRB grid. In thiscase, a boundary of a PRB is aligned with the second PRB grid. That is,the network device may determine, based on the second PRB grid, afrequency domain location of a PRB of the subcarrier spacing thatcorresponds to the second PRB grid, thereby allocating a resource to theterminal. The terminal receives data/control information on theallocated resource, or transmits data/control information on theallocated resource. In this case, the network device and the terminalhave a consistent understanding of the PRB grids, thereby ensuringcorrect interpretation of the resource and correct transmission andreception of the data/control information.

A PRB boundary of the first PRB grid is aligned with the centerfrequency of the SS. When a quantity of PRBs in the carrier is an evennumber, a PRB boundary of the second PRB grid is aligned with a centerfrequency of the carrier. If the SS raster is an integral multiple of achannel raster, in this case, the first PRB grid is aligned with thesecond PRB grid. When a quantity of PRBs in the carrier is an oddnumber, the center frequency of the carrier is aligned with a center ofone PRB in the second PRB grid. In this case, if an offset between thecenter frequency of the carrier and the center frequency of the SS is anintegral multiple of half a PRB, the first PRB grid is aligned with thesecond PRB grid.

Several cases are separately described below.

Case 1: It is assumed that a size of the SS raster is 360 kHz, a size ofthe channel raster is 180 kHz, and the subcarrier spacing of the SS is30 kHz.

A location of the center frequency of the SS is 360*n kHz, a location ofthe center frequency of the carrier is 180*m kHz, and a size of a PRBcorresponding to the subcarrier spacing of 30 kHz is 360 kHz. Afrequency offset between the center frequency of the carrier and thecenter frequency of the SS is |360*n−180*m|kHz, namely, 180*|2−m|kHz. Itis assumed that |2n−m|=k. Then, the frequency offset between the centerfrequency of the carrier and the center frequency of the SS is 180*kkHz, where m, n, and k are all non-negative integers, and “∥” representsacquisition of an absolute value.

Refer to FIG. 7 (1). When a quantity of PRBs at the subcarrier spacingof 30 kHz in the carrier is an even number, the center frequency of thecarrier is at a boundary of the second PRB grid. In this case, m is aneven number, and |2n−m| is an even number. In other words, k is an evennumber. The frequency offset between the center frequency of the carrierand the center frequency of the SS is 180*k kHz, which is an integralmultiple of the PRB size (360 kHz). In this case, the first PRB grid isaligned with the second PRB grid.

Refer to FIG. 7 (2). When the quantity of PRBs at the subcarrier spacingof 30 kHz in the carrier is an odd number, the center frequency of thecarrier is at a center of the second PRB grid, namely, at a center of anintermediate PRB. In this case, m is an odd number, and |2n−m| is an oddnumber. In other words, k is an odd number. The frequency offset betweenthe center frequency of the carrier and the center frequency of the SSis 180*k kHz that is an integral multiple of the PRB size (360 kHz) plusa remainder of ½ PRB, namely, half the PRB size. In this case, the firstPRB grid is aligned with the second PRB grid.

Therefore, regardless of whether the quantity of PRBs at the subcarrierspacing of 30 kHz in the carrier is an odd number or an even number, thefirst PRB grid can be aligned with the second PRB grid. Therefore, theindication information I₁ in this case may indicate that the frequencyoffset F₁ is 0. For example, when the indication information I₁ is “0”,it indicates that the frequency offset F₁ is 0.

Case 2: It is assumed that a size of the SS raster is 360 kHz, a size ofthe channel raster is 180 kHz, and the subcarrier spacing of the SS is15 kHz.

A location of the center frequency of the SS is 360*n kHz, a location ofthe center frequency of the carrier is 180*m kHz, and a size of a PRBcorresponding to the subcarrier spacing of 15 kHz is 180 kHz. Afrequency offset between the center frequency of the carrier and thecenter frequency of the SS is |360*n−180*m|kHz, namely, 180*|2n−m|kHz.It is assumed that |2n−m|=k. Then, the frequency offset between thecenter frequency of the carrier and the center frequency of the SS is180*k kHz, where m, n, and k are all non-negative integers, and “∥”represents acquisition of an absolute value.

Refer to FIG. 8 (1). When a quantity of PRBs at the subcarrier spacingof 15 kHz in the carrier is an even number, the center frequency of thecarrier is at a boundary of the second PRB grid. In this case, m is aneven number, and |2n−m| is an even number. In other words, k is an evennumber. The frequency offset between the center frequency of the carrierand the center frequency of the SS is 180*k kHz that is an integralmultiple of the PRB size (180 kHz). In this case, the first PRB grid isaligned with the second PRB grid.

Refer to FIG. 8 (2). When the quantity of PRBs at the subcarrier spacingof 15 kHz in the carrier is an odd number, the center frequency of thecarrier is at a center of the second PRB grid, namely, at a center of anintermediate PRB. In this case, m is an odd number, and |2n−m| is an oddnumber. In other words, k is an odd number. The frequency offset betweenthe center frequency of the carrier and the center frequency of the SSis 180*k kHz that is an integral multiple of the PRB size (180 kHz). Inthis case, the first PRB grid and the second PRB grid are not alignedwith each other, and an offset of half a PRB exists there between.

In this case, 1-bit indication information I₁ may be used to indicatethe frequency offset F₁ between the first PRB grid and the second PRBgrid. When the indication information is “0”, it indicates that thefrequency offset F₁ between the first PRB grid and the second PRB gridis 0. In other words, the first PRB grid is aligned with the second PRBgrid. When the indication information is “1”, it indicates that thefrequency offset F₁ between the first PRB grid and the second PRB gridis half a PRB. In other words, in terms of a location relationship, anoffset of half a PRB exists between the first PRB grid and the secondPRB grid. Certainly, content indicated by “0” and content indicated by“1” may be reversed, and this is not limited in this application.

Case 3: It is assumed that a size of the SS raster is 180 kHz, a size ofthe channel raster is 100 kHz, and the subcarrier spacing of the SS is15 kHz.

A location of the center frequency of the SS is 180*n kHz, a location ofthe center frequency of the carrier is 100*m kHz, and a size of a PRBcorresponding to the subcarrier spacing of 15 kHz is 180 kHz. Afrequency offset between the center frequency of the carrier and thecenter frequency of the SS is |180*n−100*m| kHz, where m and n are bothnon-negative integers, and “∥” represents acquisition of an absolutevalue. In this case, the frequency offset between the center frequencyof the carrier and the center frequency of the SS varies depending onvalues of m and n. Therefore, there are a plurality of possibilities forthe frequency offset F₁ between the first PRB grid and the second PRBgrid.

In an implementation, indication information may be used to directlyindicate the frequency offset F₁ between the first PRB grid and thesecond PRB grid. In another implementation, an offset set is predefined.The offset set includes all possible values of the frequency offsetbetween the first PRB grid and the second PRB grid. In this example, theoffset set may be {0, 10, 20, 30, 40, 60, 70, 80, 90, 100, 110, 120,130, 140, 160, 170} kHz, 16 values in total. In this case, 4-bitindication information I₁ may be used to indicate a value in the offsetset. The terminal and the network device have a consistent understandingof content indicated by the indication information I₁. In addition,1-bit indication information or one indicator bit is further used toindicate an offset direction.

In addition, the frequency offset between the first PRB grid and thesecond PRB grid varies depending on different offset directions.Therefore, in an implementation, an offset in a high frequency directionor an offset in a low frequency direction may be predefined. In otherwords, the offset direction is predefined. The network device and theterminal have a consistent understanding of the offset direction. Inanother implementation, another piece of indication information I₂ isadded or 1 bit is added to the indication information, to indicate theoffset direction. For example, “0” is used to indicate offsetting in thelow frequency direction, and “1” is used to indicate offsetting in thehigh frequency direction. Certainly, content indicated by “0” andcontent indicated by “1” may be reversed, and this is not limited inthis application.

When the frequency offset between the center frequency of the carrierand the center frequency of the SS is not an integral multiple of ½ of asize of a PRB, the manner in case 3 may be used to indicate thefrequency offset F₁ between the first PRB grid and the second PRB grid.

For example, the size of the SS raster is 180 kHz, the size of thechannel raster is 100 kHz, and the subcarrier spacing of the SS is 15kHz. When the offset direction is offsetting in the low frequencydirection, the offset set may be {0, 10, 20, 30, 40, 60, 80, 90, 100,110, 120, 130, 140, 160} kHz; or when the offset direction is offsettingin the high frequency direction, the offset set may be {0, 20, 40, 60,70, 80, 90, 100, 120, 140, 160, 170} kHz.

Case 4: It is assumed that a size of the SS raster is 100 kHz, a size ofthe channel raster is 100 kHz, and the subcarrier spacing of the SS is15 kHz.

A location of the center frequency of the SS is 100*n kHz, a location ofthe center frequency of the carrier is 100*m kHz, and a size of a PRBcorresponding to the subcarrier spacing of 15 kHz is 180 kHz. Afrequency offset between the center frequency of the carrier and thecenter frequency of the SS is |100*n−100*m|kHz, where m and n are bothnon-negative integers, and “∥” represents acquisition of an absolutevalue. In this case, it may be considered that the SS raster is alignedwith the channel raster.

When a quantity of PRBs at the subcarrier spacing of 15 kHz in thecarrier is an even number, the first PRB grid is aligned with the secondPRB grid. When the quantity of PRBs at the subcarrier spacing of 15 kHzin the carrier is an odd number, an offset of 10 kHz or 90 kHz existsbetween the first PRB grid and the second PRB grid. In this case, anoffset direction may be predefined as offsetting in a high frequencydirection or offsetting in a low frequency direction. 1-bit indicationinformation I₁ is used to indicate the frequency offset F₁ between thefirst PRB grid and the second PRB grid. One value indicates that thefrequency offset is 0; in other words, there is no offset. The othervalue indicates an offset of 10 kHz or 90 kHz. Alternatively, 2-bitindication information I₁ may be used to indicate a frequency offsetvalue and an offset direction. For example, “00” indicates that thefrequency offset is 0; in other words, there is no offset. “01”indicates that the first PRB grid is offset by 10 kHz in the lowfrequency direction (or is offset by 90 kHz in the high frequencydirection), to obtain the second PRB grid. “10” indicates that the firstPRB grid is offset by 10 kHz in the high frequency direction (or isoffset by 90 kHz in the low frequency direction), to obtain the secondPRB grid.

Likewise, when the size of the SS raster is 100 kHz, the size of thechannel raster is 100 kHz, and the subcarrier spacing of the SS is 30kHz; and when a quantity of PRBs at the subcarrier spacing of 30 kHz inthe carrier is an even number, the first PRB grid is aligned with thesecond PRB grid; or when a quantity of PRBs at the subcarrier spacing of30 kHz in the carrier is an odd number, an offset of 20 kHz or 80 kHzexists between the first PRB grid and the second PRB grid. An indicationmanner is the same as in the foregoing description, and details are notdescribed herein again.

Case 5: This case is applicable to a high frequency communicationssystem, namely, a communications system in which a frequency of acarrier is higher than 6 GHz.

For example, a size of the SS raster is 2880 kHz, a size of the channelraster is 720 kHz, and the subcarrier spacing of the SS is 120 kHz. Inthis case, regardless of whether a quantity of 120 kHz PRBs in thecarrier is an odd number or an even number, an offset value between thechannel raster and the SS raster is 720*k. Therefore, it can be ensuredthat the first PRB grid is aligned with the second PRB grid, and theindication information I₁ may not be broadcast in a PBCH in a highfrequency communications system.

For another example, a size of the SS raster is 11520 kHz, a size of thechannel raster is 720 kHz, and the subcarrier spacing of the SS is 240kHz. In this case, regardless of whether a quantity of 240 kHz PRBs inthe carrier is an odd number or an even number, an offset value betweenthe channel raster and the SS raster is 720*k. It can be learned that ina high frequency communications system, the SS raster is an integralmultiple of the channel raster. Therefore, it can be ensured that thefirst PRB grid is aligned with the second PRB grid, and the indicationinformation I₁ may not be broadcast in a PBCH in a high frequencycommunications system.

In the foregoing cases, the size of the SS raster, the size of thechannel raster, and the subcarrier spacing of the SS may be determinedbased on a frequency of the carrier, for example, determined based on afrequency band in which the carrier is located. For example, a 1.8 GHzcarrier frequency band supports Case 2. In this frequency band, arelationship between the first PRB grid and the second PRB grid isindicated by using the indication information I₁. For another example, a3.5 GHz carrier frequency band supports Case 1. In this frequency band,a relationship between two PRBs may not be indicated, or a frequencyoffset of 0 is indicated, and the terminal considers by default that thefirst PRB is aligned with the second PRB. For details, refer to Table 1below.

TABLE 1 Subcarrier Carrier spacing of Channel frequency f an SS SSraster raster Indication information f < 3 GHz  15 kHz 360 kHz 180 kHzCase 2: The indication information indicates that a frequency offset is0 or half of a PRB 180 kHz 100 kHz Case 3: The indication informationindicates a frequency offset (with a plurality of values) 100 kHz 100kHz Case 4: The indication information indicates a frequency offset(with two values) 3 GHz < f < 6 GHz  30 kHz 360 kHz 180 kHz Case 1: Theindication information indicates that a frequency offset is 0, or theindication information is not sent 180 kHz 100 kHz Case 3: Theindication information indicates a frequency offset (with a plurality ofvalues) 100 kHz 100 kHz Case 4: The indication information indicates afrequency offset (with two values) 6 GHz < f < 45 GHz 120 kHz 2880 kHz 720 kHz Case 5: The indication information indicates that a frequencyoffset is 0, or the indication information is not sent f > 45 GHz 240kHz 11,520 kHz   720 kHz Case 5: The indication information indicatesthat a frequency offset is 0, or the indication information is not sent

For Case 1 and Case 5, besides a case in which the indicationinformation indicates that the frequency offset is 0, the indicationinformation I₁ may not be sent. For example, in a high frequencycommunications system, the indication information I₁ may not betransmitted by default. The terminal assumes (or considers by default)that a PRB grid used for an SS (or an SS block) is the same as (orconsistent with) a PRB grid used for a carrier.

In the foregoing table, one or more combinations of the subcarrierspacing of the SS, the SS raster, and the channel raster in differentfrequency ranges may be selected, and this is not limited in thisapplication.

In another solution of this application, the terminal assumes (orconsiders by default) that (a structure of) a PRB grid used for an SS(or an SS block) is the same as (or consistent with) (a structure of) aPRB grid used for a carrier. In this case, the terminal considers bydefault that the PRB grid used for the SS (or the SS block) is the PRBgrid used for the carrier, so as to correctly transmit and receivedata/control information on the data/control channel. In this case, thenetwork device may determine a size X of the SS raster, a size Y of thesubcarrier spacing, and a size Z of the channel raster based on thefrequency of the carrier, so that X=Z*M1, and Y*12=Z*N₁, where M1 and N1are integers greater than or equal to 2. Because the foregoing formulais met, (a structure of) the PRB grid used for the SS (or the SS block)is the same as (or consistent with) (a structure of) the PRB grid usedfor the carrier, which is consistent with the assumption of theterminal. Therefore, the terminal can correctly transmit and receivedata/control information on the data/control channel.

FIG. 9 is a schematic diagram of another communication method accordingto an embodiment of this application. In the method, a terminalconsiders by default that a PRB grid used for an SS is the same as oraligned with a PRB grid used for a carrier. As shown in FIG. 9, themethod includes the following steps:

S910. The terminal receives an SS from a network device.

S920. The terminal determines a first PRB grid based on the SS, wherethe first PRB grid is aligned (or consistent) with a PRB grid used fordata/control information transmission on a carrier.

S930. The terminal receives/transmits, by using the first PRB grid asthe PRB grid of the carrier, data/control information on the carrier.

A process in which the terminal receives the SS and determines the firstPRB grid based on the SS is the same as steps S620 and S630 in theforegoing embodiment, and details are not described herein again.

In the foregoing step S930, the terminal considers by default that a PRBgrid used for the SS is the same as or aligned with a PRB grid used forthe carrier, and the PRB grid used for the SS is used as the PRB grid ofthe carrier. Because the PRB grid used for data/control informationtransmission on the carrier is aligned with the PRB grid used for theSS, the terminal can correctly interpret a frequency resource andreceive and transmit data/control information.

FIG. 10 is a schematic diagram of still another communication methodaccording to an embodiment of this application. In the method, aterminal considers by default that a PRB grid used for an SS is the sameas or aligned with a PRB grid used for a carrier. As shown in FIG. 10,the method includes the following steps:

S101. A network device determines a size of an SS raster, a size of achannel raster, and a subcarrier spacing based on a frequency of acarrier.

S102. The network device sends an SS at a first location of the SSraster by using the determined subcarrier spacing, where a centerfrequency of the SS is located at the first location.

S103. The network device transmits or receives data/control informationon the carrier by using the determined subcarrier spacing, where a PRBgrid used for the carrier is the same as a PRB grid used for the SS.

The size of the SS raster is X, the size of the subcarrier spacing is Y,and the size of the channel raster is Z, where X=Z*M₁, Y*12=Z*N₁, and M₁and N₁ are integers greater than or equal to 2.

An NR communications system supports a plurality of subcarrier spacings,such as {3.75, 7.5, 15, 30, 60, 120, 240, 480} kHz. A plurality ofsubcarrier spacings can be supported on one carrier, and PRBscorresponding to different subcarrier spacings are located on PRB grids.In other words, there are different PRB grids for different subcarrierspacings. PRB grids corresponding to different subcarrier spacings arein a nesting relationship in frequency domain. For example, FIG. 11 is aschematic diagram of PRB grids corresponding to a plurality ofsubcarrier spacings according to an embodiment of this application,where f₀, 2f₀, 4f₀, and 8f₀ on a left side represent subcarrierspacings, and grids corresponding to these subcarrier spacings representPRB grids for corresponding subcarrier spacings. It can be learned thatPRB grids corresponding to different subcarrier spacings are in anesting relationship in frequency domain. After determining a PRB gridcorresponding to a subcarrier spacing, a terminal cannot determineanother PRB grid corresponding to a subcarrier spacing that is greaterthan the subcarrier spacing. For example, as shown in FIG. 11, aboundary of a PRB grid corresponding to the subcarrier spacing f₀ mayfall on a boundary of a PRB grid corresponding to the subcarrier spacing2f₀, or may fall at a center of a PRB in a PRB grid corresponding to thesubcarrier spacing 2f₀. Therefore, the terminal cannot determine the PRBgrid corresponding to the subcarrier spacing 2f₀. If the terminaldetermines the PRB grid corresponding to the subcarrier spacing 2f₀, theboundary of the PRB grid corresponding to the subcarrier spacing f₀ isonly on the boundary of the PRB grid corresponding to the subcarrierspacing 2f₀. Therefore, the PRB grid corresponding to the subcarrierspacing f₀ may be directly determined based on the subcarrier spacingf₀.

In consideration of this problem, an embodiment of this applicationprovides another communication method. In the method, a network devicesends indication information I₃ to a terminal, where the indicationinformation I₃ is used to indicate a frequency offset between PRB gridscorresponding to different subcarrier spacings. In this way, theterminal can determine an unknown PRB grid based on a known PRB grid andthe frequency offset. The known PRB grid may be the PRB grid G₁ in theforegoing embodiments. In other words, a subcarrier spacingcorresponding to the known PRB grid is the same as a subcarrier spacingof an SS. Therefore, a method for obtaining the known PRB grid is thesame as a method for obtaining the PRB grid G₁ in the foregoingembodiments. Details are not described herein again.

FIG. 12 is a schematic diagram of yet another communication methodaccording to an embodiment of this application. As shown in FIG. 12, themethod includes the following steps:

S121. A terminal determines a PRB grid D₁, where a subcarrier spacingcorresponding to the PRB grid D₁ is S₁.

S122. A network device sends indication information I₃ to the terminal,where the indication information is used to indicate a frequency offsetF₂ between the PRB grid D₁ and a PRB grid D₂, a subcarrier spacingcorresponding to the PRB grid D₂ is S₂, and the subcarrier spacing S₂ isgreater than the subcarrier spacing S₁. The terminal receives theindication information I₃ from the network device, and performs thefollowing step S123.

S123. The terminal determines the PRB grid D₂ based on the PRB grid D₁and the frequency offset F₂.

Then data/control information transmission (S124) is performed betweenthe terminal and the network device. The network device allocates aresource for the data/control information transmission to the terminalbased on the PRB grid D₂. After the terminal determines the PRB grid D₂,the terminal has a consistent understanding of the resource as thenetwork device, thereby improving correctness of the data/controlinformation transmission.

The PRB grid D₁ may be the PRB grid G₁ in the foregoing embodiments. Theterminal may determine the PRB grid D₁ by using a method in theforegoing embodiments. Details are not described herein again.Alternatively, the terminal considers by default that the PRB grid D₁ (aPRB grid G₁) is the same as (or consistent with) a PRB grid (a PRB gridG₀) used for an SS (or an SS block). After detecting the SS, theterminal directly determines the PRB grid D₁ based on the detected SS.

The subcarrier spacing S₁ corresponding to the PRB grid D₁ may be thesubcarrier spacing of the SS. The subcarrier spacing S₂ corresponding tothe PRB grid D₂ is greater than the subcarrier spacing of the SS.

The network device may send the indication information I₃ through aPBCH, and then the terminal may receive the indication information I₃through the PBCH. Alternatively, the network device may send theindication information I₃ by using remaining minimum system information(RMSI), and then the terminal receives the RMSI, where the RMSI carriesthe indication information I₃. Alternatively, the network device maysend the indication information I₃ by using higher layer signaling, forexample, a radio resource control (RRC) message, and then the terminalreceives the higher layer signaling, where the higher layer signalingcarries the indication information I₃.

The method in this embodiment can be combined with the methods in theforegoing embodiments. When a carrier supports a plurality of subcarrierspacings, the plurality of subcarrier spacings include the subcarrierspacing S₁ and the subcarrier spacing 52, where the subcarrier spacingS₁ is the same as the subcarrier spacing of the SS, and the subcarrierspacing S₂ is different from the subcarrier spacing of the SS. Whendetecting the SS, the terminal may determine a PRB grid used for the SSbased on the SS. When the terminal considers by default that a PRB gridused for an SS is the same as a PRB grid used for a carrier, the PRBgrid of the SS may be used as the PRB grid D₁. When the terminaldetermines a PRB grid used for the carrier based on the indicationinformation I₁ sent by the network device, the terminal determines thePRB grid D₁ based on the indication information I₁ in the foregoingembodiments; and then determines the PRB grid D₂ based on the PRB gridD₁ and the indication information I₃. In this way, correct transmissionof data/control information on a carrier that supports the subcarrierspacings S₁ and S₂ can be implemented. More subcarrier spacings aresimilar thereto, and details are not described herein again.

The terminal considers by default that the PRB grid D₁ (a PRB grid G₁)is the same as a PRB grid G₀ used for an SS (or an SS block). Afterdetecting the SS, the terminal determines the PRB grid D₂ based on thedetected SS. FIG. 13 is a schematic diagram of another communicationmethod according to an embodiment of this application. As shown in FIG.13, the method includes the following steps:

S131. A network device sends an SS to a terminal.

S132. The terminal detects the SS.

S133. When the SS is detected, the terminal determines a centerfrequency of the SS.

S134. The network device sends indication information I₄ to theterminal, where the indication information I₄ is used to indicate afrequency offset F₃ between the center frequency of the SS and aboundary of a PRB grid D₂.

S135. The terminal determines the PRB grid D₂ based on the centerfrequency of the SS and the frequency offset F₃.

Then data/control information transmission (S136) is performed betweenthe terminal and the network device. The network device allocates aresource for the data/control information transmission to the terminalbased on the PRB grid D₂. After the terminal determines the PRB grid D₂,the terminal has a consistent understanding of the resource as thenetwork device, thereby improving correctness of the data/controlinformation transmission.

A subcarrier spacing S₂ corresponding to the PRB grid D₂ is greater thana subcarrier spacing of the SS.

The network device may send the indication information I₄ through aPBCH, and then the terminal may receive the indication information I₄through the PBCH. Alternatively, the network device may send theindication information I₄ by using RMSI, and then the terminal receivesthe RMSI, where the RMSI carries the indication information I₄.Alternatively, the network device may send the indication information I₄by using higher layer signaling, for example, an RRC message, and thenthe terminal receives the higher layer signaling, where the higher layersignaling carries the indication information I₄.

FIG. 14 is a schematic diagram of a PRB grid according to an embodimentof this application. It is assumed that a subcarrier spacingcorresponding to a PRB grid D₁ or a subcarrier spacing of an SS is areference subcarrier spacing f₀, and a subcarrier spacing correspondingto a PRB grid D₂ is f₁. As shown in FIG. 14 (1), f₁/f₀=2. For theembodiment shown in FIG. 12, a boundary of the PRB grid D₁ may belocated at a boundary (for example, a location 0 in FIG. 14 (1)) of thePRB grid D₂, or may be located at a center (for example, a location 1 inFIG. 14 (1)) of a PRB of the PRB grid D₂. In this case, i-bit indicationinformation I₃ may be used to indicate the location. For example, “0”indicates the location 0, and “1” indicates the location 1. Certainly,meanings of values of the indication information I₃ may also bereversed, and this is not limited. For the embodiment shown in FIG. 13,a center frequency of the SS (or an SS block) may be located at aboundary (for example, a location 0 in FIG. 14 (1)) of the PRB grid D₂,or may be located at a center (for example, a location 1 in FIG. 14 (1))of a PRB of the PRB grid D₂. In this case, i-bit indication informationI₄ may be used to indicate the location. For example, “0” indicates thelocation 0, and “1” indicates the location 1. Certainly, meanings ofvalues of the indication information I₄ may also be reversed, and thisis not limited. The foregoing locations may be indicated by using afrequency offset. To be specific, the location 0 indicates that afrequency offset F₂ or F₃ is 0, and the location 1 indicates that thefrequency offset F₂ or F₃ is half a PRB. A subcarrier spacingcorresponding to the PRB is the same as the subcarrier spacingcorresponding to the PRB grid D₂.

As shown in FIG. 14 (2), f₁/f₀=4. For the embodiment shown in FIG. 12, aboundary of the PRB grid D₁ may be located at a boundary (for example, alocation 0 in FIG. 14 (2)) of the PRB grid D₂, or may be located at alocation (for example, a location 1 in FIG. 14 (2)) that is ¼ of a PRBof the PRB grid D₂, or may be located at a center (for example, alocation 2 in FIG. 14 (2)) of a PRB of the PRB grid D₂, or may belocated at a location (for example, a location 3 in FIG. 14 (2)) that is¾ of a PRB of the PRB grid D₂. In this case, 2-bit indicationinformation I₃ may be used to indicate the location. For example, “00”indicates the location 0, “01” indicates the location 1, “10” indicatesthe location 2, and “11” indicates the location 3. For the embodimentshown in FIG. 13, a center frequency of the SS (or an SS block) may belocated at a boundary (for example, a location 0 in FIG. 14 (2)) of thePRB grid D₂, or may be located at a location (for example, a location 1in FIG. 14 (2)) that is ¼ of a PRB of the PRB grid D₂, or may be locatedat a center (for example, a location 2 in FIG. 14 (2)) of a PRB of thePRB grid D₂, or may be located at a location (for example, a location 3in FIG. 14 (2)) that is ¾ of a PRB of the PRB grid D₂. In this case,2-bit indication information I₄ may be used to indicate the location.For example, “00” indicates the location 0, “01” indicates the location1, “10” indicates the location 2, and “11” indicates the location 3. Theforegoing locations may be indicated by using a frequency offset. To bespecific, the location 0 indicates that a frequency offset F₂ or F₃ is0, the location 1 indicates that the frequency offset F₂ or F₃ is ¼ of aPRB, the location 2 indicates that the frequency offset F₂ or F₃ is ½ ofa PRB, and the location 3 indicates that the frequency offset F₂ or F₃is ¾ of a PRB. A subcarrier spacing corresponding to the PRB is the sameas the subcarrier spacing corresponding to the PRB grid D₂. Possiblelocation numbers of a PRB in the PRB grid D₂ may be predefined from alow frequency domain location number to a high frequency domain locationnumber, or predefined from a high frequency domain location number to alow frequency domain location number. Alternatively, 1 bit is used toindicate a numbering direction, namely, an offset direction.

As described in the foregoing embodiments, the PRB grid D₂ may be usedfor data/control information transmission. For example, the PRB grid D₂may be used for RMSI transmission. In this case, the PRB grid D₂ is aPRB grid of the RMSI. Therefore, any method for determining the PRB gridD₂ provided in the foregoing embodiments may be used to determine thePRB grid of the RMSI. The PRB grid of the RMSI is a PRB gridcorresponding to a subcarrier spacing that is used to transmit the RMSI.In this case, the subcarrier spacing of the RMSI is the subcarrierspacing S₂ corresponding to the PRB grid D₂. The following is describedwith reference to the accompanying drawings by using an example in whichthe PRB grid D₂ is the PRB grid of the RMSI.

FIG. 24 is a schematic diagram of a still another communication methodaccording to an embodiment of this application. As shown in FIG. 24, themethod includes the following steps.

S241. A network device sends an SS block.

The SS block includes an SS and a PBCH, where information about asubcarrier spacing S₂ of RMSI is carried on the PBCH.

S242. The terminal detects an SS, and receives information on a PBCH.

After detecting the SS, the terminal may determine a center frequency ofthe SS, and then receive, on 24 PRBs that center on the centerfrequency, the information on the PBCH. In this way, the terminal mayobtain the subcarrier spacing S₂ of the RMSI. Because the subcarrierspacing S₂ of the RMSI may be different from a subcarrier spacing of theSS, as described in the foregoing embodiments, when the subcarrierspacing S₂ of the RMSI is greater than the subcarrier spacing of the SS,the network device indicates a frequency offset F₂ between a PRB grid D₁and a PRB grid D₂ to the terminal, so that the terminal determines thePRB grid D₂ of the RMSI based on the PRB grid D₁. For example, thenetwork device sends indication information I₀ to the terminal, wherethe indication information is used to determine a PRB grid of the RMSI.In this case, the method further includes the following steps:

S243. The network device sends indication information I₀ to theterminal, where the indication information is used to determine a PRBgrid of RMSI.

The network device may send the indication information I₀ through thePBCH.

S244. The terminal receives the indication information I₀, anddetermines the PRB grid of the RMSI based on the indication informationI₀.

Specifically, the terminal determines the PRB grid D₁ by using anymethod in the foregoing embodiments, and then determines the PRB grid ofthe RMSI based on the PRB grid D₁ and the indication information I₀.

S245. The terminal receives the RMSI based on the determined PRB grid ofthe RMSI.

Several implementation solutions of the indication information I₀ areseparately described below. These implementation solutions of theindication information I₀ are applicable to any one of the foregoingsolutions for determining the PRB grid D₂. The PRB grid D₂ is, forexample, the PRB grid of the RMSI in FIG. 24.

Solution 1: The indication information indicates a relative locationbetween the PRB grid D₁ and the PRB grid D₂.

The indication information I₀ may include two information bits. Fordifferent subcarrier spacings S₁ corresponding to the PRB grid D₁ anddifferent subcarrier spacings S₂ corresponding to the PRB grid D₂,explanations of the two information bits are different.

FIG. 25 is a schematic diagram of a PRB grid according to an embodimentof this application. It is assumed that a subcarrier spacingcorresponding to a PRB grid D₁ is a reference subcarrier spacing f₀, andthe subcarrier spacing is equal to a subcarrier spacing of an SS; and asubcarrier spacing corresponding to a PRB grid D₂ is f₁. As shown inFIG. 25, FIG. 25 (1) shows an example in which the subcarrier spacing f₀is 15 kHz and the subcarrier spacing f₁ is 30 kHz, and FIG. 25 (2) showsan example in which the subcarrier spacing f₀ is 30 kHz and thesubcarrier spacing f₁ is 60 kHz, where f₁/f₀=2. In this case, a boundaryof the PRB grid D₁ (using a boundary B₁ in FIG. 25 as an example) may belocated at a boundary (indicated by a location 0 in FIG. 25) of the PRBgrid D₂, or may be located at a center (indicated by a location 1 inFIG. 25) of a PRB of the PRB grid D₂.

In this case, 2-bit indication information I₀ may be used to indicatethe grid location. For example, “00” indicates the location 0, “01”indicates the location 1, and “10” and “11” are used as reservedinformation bits. Certainly, there may also be another explanation formeanings of values of the indication information I₀. For example, “10”indicates the location 0, “11” indicates the location 1, and “00” and“01” are used as reserved information bits. This is not limited. Theforegoing grid location may be indicated by using a frequency domainoffset. To be specific, “00” indicates that the frequency domain offsetis 0, and “01” indicates that the frequency domain offset is half a PRBor six subcarriers, where a subcarrier spacing corresponding to the PRBor the subcarriers is the same as the subcarrier spacing correspondingto the PRB grid D₂. Alternatively, “00” indicates that the frequencydomain offset is 0, and “01” indicates that the offset is one PRB or 12subcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is the same as the subcarrier spacing corresponding to thePRB grid D₁.

FIG. 26 is a schematic diagram of another PRB grid according to anembodiment of this application. It is assumed that a subcarrier spacingcorresponding to a PRB grid D₁ is a reference subcarrier spacing f₀, andthe subcarrier spacing is equal to a subcarrier spacing of an SS; and asubcarrier spacing corresponding to a PRB grid D₂ is f₁. As shown inFIG. 26, in an example in which the subcarrier spacing f₀ is 15 kHz, andthe subcarrier spacing f₁ is 60 kHz and f₁/f₀=4, a boundary (forexample, a boundary B2 in FIG. 26) of the PRB grid D₁ may be located ata boundary (indicated by a location 0 in FIG. 26) of the PRB grid D₂, ormay be located at a location (indicated by a location 1 in FIG. 26) thatis ¼ of a PRB of the PRB grid D₂, or may be located at a center(indicated by a location 2 in FIG. 26) of a PRB of the PRB grid D₂, ormay be located at a location (indicated by a location 3 in FIG. 26) thatis ¾ of a PRB of the PRB grid D₂. A frequency domain offset directionmay be predefined as that a boundary B1 offsets from a low frequencydomain location to a high frequency domain location, or may bepredefined as that a boundary B1 offsets from a high frequency domainlocation to a low frequency domain location, or 1 bit is used toindicate the offset direction.

In this case, 2-bit indication information I₀ may be used to indicatethe grid location. For example, “00” indicates the location 0, “01”indicates the location 1, “10” indicates the location 2, and “11”indicates the location 3. Certainly, there may also be anotherexplanation for meanings of values of the indication information I₀, andthis is not limited. The foregoing grid location may be indicated byusing a frequency domain offset. For example, “00” indicates that thefrequency domain offset is 0, “01” indicates that the frequency domainoffset is ¼ of a PRB or three subcarriers, “10” indicates that thefrequency domain offset is ½ of a PRB or six subcarriers, and “11”indicates that the frequency domain offset is ¾ of a PRB or ninesubcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is the same as the subcarrier spacing corresponding to thePRB grid D₂. Alternatively, “00” indicates that the frequency domainoffset is 0, “01” indicates that the frequency domain offset is one PRBor 12 subcarriers, “10” indicates that the frequency domain offset istwo PRBs or 24 subcarriers, and “11” indicates that the frequency domainoffset is three PRBs or 36 subcarriers, where a subcarrier spacingcorresponding to the PRB or the subcarriers is the same as thesubcarrier spacing corresponding to the PRB grid D₁. A frequency domainoffset direction may be predefined as that the boundary B2 offsets froma low frequency domain location to a high frequency domain location, ormay be predefined as that the boundary B2 offsets from a high frequencydomain location to a low frequency domain location, or 1 bit is used toindicate the offset direction.

In addition, an offset (an offset shown in FIG. 26) exists between aboundary of the foregoing PRB grid D₁ and a center frequency of the SS.This offset may be “0”. In this case, a PRB grid of the SS may be usedas the PRB grid D₁.

It can be learned that in this solution, the indication information I₀may be used to indicate a relative location between the PRB grid D₁ andthe PRB grid D₂, where the relative location may be a frequency domainoffset or a location of a preset boundary of the PRB grid D₁ on the PRBgrid D₂.

Solution 2: The indication information indicates a PRB gridcorresponding to a maximum subcarrier spacing that is supported by acarrier frequency band, so as to implicitly obtain the PRB grid D₂.

The indication information I₀ may include two information bits, used toindicate a PRB grid corresponding to a maximum subcarrier spacing thatis supported by a carrier frequency band. For example, in a carrierbelow 6 GHz, regardless of a size of a subcarrier of the RMSI, theindication information is used to indicate a PRB grid corresponding to 6o kHz.

If the subcarrier spacing of the SS is 15 kHz, the subcarrier spacingcorresponding to the PRB grid D₁ is 15 kHz. In this case, the indicationinformation I₀ indicates a relative location between a PRB grid D₂′corresponding to the maximum subcarrier spacing that is supported by thecarrier frequency band and the PRB grid D₁, where the relative locationmay be a frequency domain offset, or a location of a boundary of the PRBgrid D₁ on the PRB grid D₂′. For example, if the indication informationI₀ is “00”, it indicates that the frequency domain offset is 0, “01”indicates that the frequency domain offset is ¼ of a PRB or threesubcarriers, “10” indicates that the frequency domain offset is ½ of aPRB or six subcarriers, and “11” indicates that the frequency domainoffset is ¾ of a PRB or nine subcarriers, where a subcarrier spacingcorresponding to the PRB or the subcarriers is a maximum subcarrierspacing (60 kHz) supported by a current carrier frequency band.Alternatively, if the indication information I₀ is “00”, it indicatesthat the frequency domain offset is 0, “01” indicates that the frequencydomain offset is one PRB or 12 subcarriers, “10” indicates that thefrequency domain offset is two PRBs or 24 subcarriers, and “ii”indicates that the frequency domain offset is three PRBs or 36subcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is the subcarrier spacing of the SS. A frequency domainoffset direction may be predefined as that a boundary B2 in the PRB gridD₁ offsets from a low frequency domain location to a high frequencydomain location, or may be predefined as that a boundary B2 in the PRBgrid D₁ offsets from a high frequency domain location to a low frequencydomain location, or 1 bit is used to indicate the offset direction.

If the subcarrier spacing of the SS is 30 kHz, the subcarrier spacingcorresponding to the PRB grid D₁ is 30 kHz. In this case, the indicationinformation I₀ indicates a relative location between a PRB grid D₂″corresponding to the maximum subcarrier spacing that is supported by thecarrier frequency band and the PRB grid D₁, where the relative locationmay be a frequency domain offset, or a location of a boundary of the PRBgrid D₁ on the PRB grid D₂″. For example, if the indication informationI₀ is “00”, it indicates that the frequency domain offset is 0, and “01”indicates that the frequency domain offset is half a PRB or sixsubcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is a maximum subcarrier spacing (60 kHz) supported by acurrent carrier frequency band. Alternatively, if the indicationinformation I₀ is “00”, it indicates that the frequency domain offset is0, and “01” indicates that the frequency domain offset is one PRB or 12subcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is the same as the subcarrier spacing of the SS. A frequencydomain offset direction may be predefined as that a boundary B1 in thePRB grid D₁ offsets from a low frequency domain location to a highfrequency domain location, or may be predefined as that a boundary B1 inthe PRB grid D₁ offsets from a high frequency domain location to a lowfrequency domain location, or 1 bit is used to indicate the offsetdirection.

There may also be another explanation for meanings of values of theindication information I₀, and this is not limited.

When the PRB grid corresponding to the maximum subcarrier spacing thatis supported by the current carrier frequency band is determined, thePRB grid D₂ may be determined based on a nesting relationship betweendifferent subcarrier spacings shown in FIG. 11.

It can be learned that in this solution, the indication information I₀may be used to indicate a PRB grid corresponding to a maximum subcarrierspacing that is supported by a carrier frequency band, for example,indicate a relative location between the PRB grid D₁ and the PRB gridcorresponding to the maximum subcarrier spacing that is supported by thecarrier frequency band, where the relative location may be a frequencydomain offset, or a location of a preset boundary of the PRB grid D₁ onthe PRB grid corresponding to the maximum subcarrier spacing that issupported by the carrier frequency band.

Solution 3: The indication information indicates a relative locationbetween the PRB grid D₁ and the PRB grid D₂.

In an initial access process, RMSI is used for a terminal to access acarrier. In this case, the subcarrier spacing of the RMSI is supportedby all terminals. In a frequency band below 6 GHz, a 60 kHz subcarrierspacing may not be applicable to all terminals, and a candidatesubcarrier spacing of the RMSI may be only 15 kHz or 30 kHz. In thiscase, i-bit second indication information I₀ may be sent on the PBCH, toindicate a PRB grid corresponding to the subcarrier spacing of the RMSI.

For example, if the indication information I₀ is “0”, it indicates thata frequency domain offset is 0, and “1” indicates that the offset ishalf a PRB or six subcarriers, where a subcarrier spacing correspondingto the PRB or the subcarriers is the subcarrier spacing of the RMSI.Alternatively, if the indication information I₀ is “0”, it indicatesthat the frequency domain offset is 0, and “1” indicates that thefrequency domain offset is one PRB or 12 subcarriers, where a subcarrierspacing corresponding to the PRB or the subcarriers is the same as thesubcarrier spacing of the SS. A frequency domain offset direction may bepredefined as that a boundary B1 or B2 in the PRB grid D₁ offsets from alow frequency domain location to a high frequency domain location, ormay be predefined as that a boundary B1 or B2 in the PRB grid D₁ offsetsfrom a high frequency domain location to a low frequency domainlocation, or 1 bit is used to indicate the offset direction.

There may also be another explanation for meanings of values of theindication information I₀, and this is not limited.

It can be learned that in this solution, there are two candidatesubcarrier spacings of the RMSI, and the indication information I₀includes one information bit, and may be used to indicate a relativelocation between the PRB grid D₁ and the PRB grid D₂, where the relativelocation may be a frequency domain offset, or a location of a presetboundary of the PRB grid D₁ on the PRB grid D₂.

Solution 4: The indication information jointly indicates the subcarrierspacing of the RMSI and the PRB grid of the RMSI.

In an initial access process, RMSI is used for a terminal to access acarrier. In this case, the subcarrier spacing of the RMSI is supportedby all terminals. In a frequency band below 6 GHz, a 60 kHz subcarrierspacing may not be applicable to all terminals, and a candidatesubcarrier spacing of the RMSI is only 15 kHz or 30 kHz. In this case,2-bit indication information I₀ may be sent on the PBCH, to indicate thesubcarrier spacing of the RMSI and the PRB grid of the RMSI.

When the subcarrier spacing S₁ of the SS is 15 kHz, the subcarrierspacing of the RMSI is 52, and meanings of values of the indicationinformation I₀ may be shown in Table 3 below:

TABLE 3 I0 S2 00 15 kHz 01 30 kHz, where a grid boundary is a candidatelocation 1 10 30 kHz, where a grid boundary is a candidate location 2 11Reserved

The candidate locations in the table may be shown in FIG. 25 (1), andare respectively a location 0 and a location 1. The candidate location 1may be the location 0, and the candidate location 2 may be the location1; or the candidate location 1 may be the location 1, and the candidatelocation 2 may be the location 0.

The foregoing locations may also be indicated by using a frequencydomain offset, as shown in Table 4 below:

TABLE 4 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 10 30 kHz, and offset by one PRB (where a subcarrierspacing is S1) 11 Reserved

Alternatively, as shown in Table 5 below:

TABLE 5 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 10 30 kHz, and offset by 1/2 of a PRB (where a subcarrierspacing is S2) 11 Reserved

When the subcarrier spacing S₁ of the SS is 30 kHz, the subcarrierspacing of the RMSI is S₂. When the subcarrier spacing S₂ of the RMSI issmaller than the subcarrier spacing S₁ of the SS, the PRB grid of theRMSI may be obtained based on a nesting relationship shown in FIG. 11.In this case, the indication information I₀ may be used only to indicatea subcarrier spacing, and meanings of values of the indicationinformation I₀ may be shown in Table 6 below:

TABLE 6 I0 S2 00 15 kHz 01 30 kHz 10 Reserved 11 Reserved

The foregoing locations may be indicated by using a frequency domainoffset, as shown in Table 7 or Table 8 below. Because a quantity of PRBsoffset in this case is 0, the indication information I₀ may be used onlyto indicate a subcarrier spacing.

TABLE 7 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 10 Reserved 11 Reserved

TABLE 8 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 10 Reserved 11 Reserved

The offset in the table is an offset from a boundary B1 or B2 in the PRBgrid D₁ to the PRB grid D₂. A frequency domain offset direction may bepredefined as offsetting from a low frequency domain location to a highfrequency domain location, or may be predefined as offsetting from ahigh frequency domain location to a low frequency domain location, or 1bit is used to indicate the offset direction. A unit of the offset mayalternatively be a quantity of subcarriers, and one PRB corresponds to12 subcarriers.

It can be learned that in this solution, there are two candidatesubcarrier spacings of the RMSI, and the indication information I₀includes two information bits, and may be used to indicate thesubcarrier spacing of the RMSI, or may be used to indicate thesubcarrier spacing of the RMSI and a relative location between the PRBgrid D₁ and the PRB grid D₂, where the relative location may be afrequency domain offset, or a location of a preset boundary of the PRBgrid D₁ on the PRB grid D₂.

Solution 5: The indication information jointly indicates the subcarrierspacing of the RMSI and the PRB grid of the RMSI.

A difference from Solution 4 is that a candidate subcarrier spacing ofthe RMSI is not limited. In this case, the indication information I₀includes three information bits, and is used to indicate the subcarrierspacing of the RMSI and a relative location between the PRB grid D₁ andthe PRB grid D₂, where the relative location may be a frequency domainoffset, or a location of a preset boundary of the PRB grid D₁ on the PRBgrid D₂.

For subcarrier spacings S₁ of different SSs, explanations of values ofthe indication information I₀ are different. When S₁ is 15 kHz, meaningsof the indication information I₀ are shown in Table 9 below:

TABLE 9 I0 S2 000 15 kHz 001 30 kHz, where a grid boundary is acandidate location 0 010 30 kHz, where a grid boundary is a candidatelocation 1 011 60 kHz, where a grid boundary is a candidate location 0100 60 kHz, where a grid boundary is a candidate location 1 101 60 kHz,where a grid boundary is a candidate location 2 110 60 kHz, where a gridboundary is a candidate location 3 111 Reserved

When S₂ is 30 kHz, candidate locations in the table may be shown in FIG.25 (1), and are respectively a location 0 and a location 1. Thecandidate location 0 may be the location 0, and the candidate location 1may be the location 1; or the candidate location 0 may be the location1, and the candidate location 1 may be the location 0. When S₂ is 60kHz, candidate locations in the table may be shown in FIG. 26, and arerespectively locations 0 to 3. The candidate location 0 may be alocation 0, the candidate location 1 may be a location 1, the candidatelocation 2 may be a location 2, and the candidate location 3 may be alocation 3. Certainly, the candidate locations 0 to 3 may alternativelycorrespond to the locations 0 to 3 in FIG. 26 in another form, and thisis not limited in this application.

The foregoing locations may be indicated by using a frequency domainoffset, as shown in Table 10 or Table 11 below:

TABLE 10 I0 S2 000 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 001 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 010 30 kHz, and offset by one PRB (where a subcarrierspacing is S1) 011 60 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 100 60 kHz, and offset by one PRB (where a subcarrierspacing is S1) 101 60 kHz, and offset by two PRBs (where a subcarrierspacing is S1) 110 60 kHz, and offset by three PRBs (where a subcarrierspacing is S1) 111 Reserved

TABLE 11 I0 S2 000 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 001 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 010 30 kHz, and offset by 1/2 of a PRB (where asubcarrier spacing is S2) 011 60 kHz, and offset by zero PRBs (where asubcarrier spacing is S2) 100 60 kHz, and offset by 1/4 of a PRB (wherea subcarrier spacing is S2) 101 60 kHz, and offset by 1/2 PRB (where asubcarrier spacing is S2) 110 60 kHz, and offset by 3/4 of a PRB (wherea subcarrier spacing is S2) 111 Reserved

When S₁ is 30 kHz, meanings of the indication information I₀ are shownin Table 12 below:

TABLE 12 I0 S2 000 15 kHz 001 30 kHz 010 60 kHz, where a grid boundaryis a candidate location 1 011 60 kHz, where a grid boundary is acandidate location 2 100 Reserved 101 Reserved 110 Reserved 111 Reserved

When S₂ is 60 kHz, candidate locations in the table may be shown in FIG.25 (2), and are respectively a location 0 and a location 1. Thecandidate location 1 may be the location 0, and the candidate location 2may be the location 1; or the candidate location 1 may be the location1, and the candidate location 2 may be the location 0.

The foregoing locations may be indicated by using a frequency domainoffset, as shown in Table 13 or Table 14 below:

TABLE 13 I0 S2 000 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 001 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 010 60 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 011 60 kHz, and offset by one PRB (where a subcarrierspacing is S1) 100 Reserved 101 Reserved 110 Reserved 111 Reserved

TABLE 14 I0 S2 000 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 001 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 010 60 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 011 60 kHz, and offset by 1/2 of a PRB (where asubcarrier spacing is S2) 100 Reserved 101 Reserved 110 Reserved 111Reserved

The offset in the table is an offset from a boundary B1 or B2 in the PRBgrid D₁ to the PRB grid D₂. A frequency domain offset direction may bepredefined as offsetting from a low frequency domain location to a highfrequency domain location, or may be predefined as offsetting from ahigh frequency domain location to a low frequency domain location, or 1bit is used to indicate the offset direction. A unit of the offset mayalternatively be a quantity of subcarriers, and one PRB corresponds to12 subcarriers.

Solution 6: The subcarrier spacing of the RMSI is limited, and reuseindication information of the RMSI to indicate the PRB grid of the RMSIwithout adding an extra bit.

The indication information of the RMSI is used to indicate thesubcarrier spacing of the RMSI. Different carrier frequency bandssupport limited subcarrier spacing sets. For example, in a carrierfrequency band below 6 GHz, {15, 30, 60} kHz is supported, and in acarrier frequency band above 6 GHz, {120, 240} kHz is supported.Therefore, when the network device indicates the subcarrier spacing S₂of the RMSI to the terminal device, a requirement can be met by usingtwo information bits. In this solution, by limiting a candidate set ofthe subcarrier spacing S₂, the PRB grid D₂ corresponding to the datasubcarrier spacing S₂ is notified to the terminal without adding a bit.

When the subcarrier spacing S₁ of the SS is 15 kHz, the candidate set ofthe subcarrier spacing S₂ is limited to {15, 30} kHz, and then thenetwork device sends the indication information I₀ to the terminal onthe PBCH, and the terminal determines, based on the indicationinformation I₀ and the PRB grid D₁ corresponding to the subcarrierspacing S₁, the PRB grid D₂ corresponding to the subcarrier spacing S₂.Specific bit information of the indication information I₀ is shown inTable 15 below:

TABLE 15 I0 S2 00 15 kHz 01 30 kHz, where a grid boundary is a candidatelocation 1 10 30 kHz, where a grid boundary is a candidate location 2 11Reserved

When S₂ is 30 kHz, candidate locations in the table may be shown in FIG.25 (1), and are respectively a location 0 and a location 1. Thecandidate location 1 may be the location 0, and the candidate location 2may be the location 1; or the candidate location 1 may be the location1, and the candidate location 2 may be the location 0.

The foregoing locations may be indicated by using a frequency domainoffset, as shown in Table 16 or Table 17 below:

TABLE 16 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 10 30 kHz, and offset by one PRB (where a subcarrierspacing is S1) 11 Reserved

TABLE 17 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 10 30 kHz, and offset by 1/2 of a PRB (where a subcarrierspacing is S2) 11 Reserved

When the subcarrier spacing S₁ of an SS block is 30 kHz, specific bitinformation of the indication information I₀ is shown in Table 18 below:

TABLE 18 I0 S2 00 15 kHz 01 30 kHz 10 60 kHz, where a grid boundary is acandidate location 1 11 60 kHz, where a grid boundary is a candidatelocation 2

When S₂ is 60 kHz, candidate locations in the table may be shown in FIG.25 (2), and are respectively a location 0 and a location 1. Thecandidate location 1 may be the location 0, and the candidate location 2may be the location 1; or the candidate location 1 may be the location1, and the candidate location 2 may be the location 0.

The foregoing locations may be indicated by using a frequency domainoffset, as shown in Table 19 or Table 20 below:

TABLE 19 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 10 60 kHz, and offset by zero PRBs (where a subcarrierspacing is S1) 11 60 kHz, and offset by one PRB (where a subcarrierspacing is S1)

TABLE 20 I0 S2 00 15 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 01 30 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 10 60 kHz, and offset by zero PRBs (where a subcarrierspacing is S2) 11 60 kHz, and offset by 1/2 of a PRB (where a subcarrierspacing is S2)

The offset in the table is an offset from a boundary B1 or B2 in the PRBgrid D₁ (corresponding to the subcarrier spacing S₁) to the PRB grid D₂(corresponding to the subcarrier spacing S₂). A frequency domain offsetdirection may be predefined as offsetting from a low frequency domainlocation to a high frequency domain location, or may be predefined asoffsetting from a high frequency domain location to a low frequencydomain location, or 1 bit is used to indicate the offset direction. Aunit of the offset may alternatively be a quantity of subcarriers, andone PRB corresponds to 12 subcarriers.

Optionally, the network device may notify, in the RMSI or an RRCmessage, a PRB grid corresponding to a maximum subcarrier spacing thatis supported by a carrier frequency band.

After the terminal receives the RMSI, the network device may sendindication information in the RMSI or higher layer signaling, forexample, an RRC message, to indicate a PRB grid corresponding to amaximum subcarrier spacing S₃ that is supported by at least one carrierfrequency band, where the subcarrier spacing may be a subcarrier spacingused to send data and/or control information. For example, in afrequency band below 6 GHz, a PRB grid of 60 kHz is indicated, and in afrequency band above 6 GHz, no indication is needed, because in thefrequency band above 6 GHz, a candidate subcarrier spacing of the SS is{120, 240} kHz, a candidate set of the subcarrier spacing used for dataand/or control information is {60, 120} kHz, and the subcarrier spacingused for data and/or control information is not greater than thesubcarrier spacing of the SS.

The indication information indicates a frequency domain offset betweenthe PRB grid corresponding to the subcarrier spacing S₃ and a known PRBgrid. The known PRB grid may be a PRB grid corresponding to thesubcarrier spacing S₁, and the subcarrier spacing S₁ may be thesubcarrier spacing of the SS, or may be a subcarrier spacing that is thesame as the subcarrier spacing of the SS and that is used for dataand/or control information transmission. Alternatively, the known PRBgrid may be a PRB grid corresponding to the subcarrier spacing of theRMSI, or a PRB grid corresponding to another known subcarrier spacing.The “known” means that the network device and the terminal have aconsistent understanding.

Optionally, the indication information may include two information bits.That is, two information bits may be used to indicate a PRB gridcorresponding to a maximum subcarrier spacing that is supported by acarrier frequency band. For example, the known PRB grid is predefined asan PRB grid corresponding to a subcarrier spacing that is the same asthe subcarrier spacing of the SS and that is used for data transmission.If the subcarrier spacing of the SS is 15 kHz, “00” indicates that thefrequency domain offset is 0, “01” indicates that the frequency domainoffset is ¼ of a PRB or three subcarriers, “10” indicates that thefrequency domain offset is ½ of a PRB or six subcarriers, and “ii”indicates that the frequency domain offset is ¾ of a PRB or ninesubcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is a maximum subcarrier spacing that is supported by acurrent carrier frequency band. Alternatively, “00” indicates that thefrequency domain offset is 0, “01” indicates that the frequency domainoffset is one PRB or 12 subcarriers, “10” indicates that the frequencydomain offset is two PRBs or 24 subcarriers, and “ii” indicates that thefrequency domain offset is three PRBs or 36 subcarriers, where asubcarrier spacing corresponding to the PRB or the subcarriers is thesubcarrier spacing of the SS.

If the subcarrier spacing of the SS is 30 kHz, “00” indicates that thefrequency domain offset is 0, and “01” indicates that the frequencydomain offset is half a PRB or six subcarriers, where a subcarrierspacing corresponding to the PRB or the subcarriers is a maximumsubcarrier spacing that is supported by a current carrier frequencyband. Alternatively, “00” indicates that the frequency domain offset is0, and “01” indicates that the frequency domain offset is one PRB or 12subcarriers, where a subcarrier spacing corresponding to the PRB or thesubcarriers is the same as the subcarrier spacing of the SS.

A frequency domain offset direction may be predefined as that a locationof a preset boundary in the PRB grid corresponding to the subcarrierspacing S₁ offsets from a low frequency domain location to a highfrequency domain location, or may be predefined as that a location of apreset boundary in the PRB grid corresponding to the subcarrier spacingS₁ offsets from a high frequency domain location to a low frequencydomain location, or 1 bit is used to indicate the offset direction.

In the foregoing solution, the subcarrier spacing of the SS is asubcarrier spacing of an SS block.

Optionally, the preset boundary in the foregoing solution may be aboundary that is aligned, after a center frequency of the SS blockoffsets by a particular quantity of subcarriers to the low frequencydomain location or the high frequency domain location, with a PRB gridof data and/or control information corresponding to the subcarrierspacing of the SS block, such as B1 in FIG. 25 or B2 in FIG. 26.

FIG. 15 is a schematic diagram of initially accessing a network by aterminal according to an embodiment of this application. As shown inFIG. 15, a process in which the terminal initially accesses the networkincludes the following steps.

S151. A network device sends an SS block, where the SS block includes anSS and a PBCH. In other words, the network device sends the SS andbroadcasts information on the PBCH.

S152. A terminal detects the SS, and determines a frequency domainlocation of the PBCH based on a center frequency of the SS and asubcarrier spacing of the SS when the SS is detected. For example, 24PRBs that center on the center frequency of the SS are frequency domainlocation of the PBCH, and a subcarrier spacing corresponding to the PRBsis the subcarrier spacing of the SS. In this way, the terminal canreceive the information on the PBCH at the frequency domain location ofthe PBCH.

S154. The network device sends RMSI.

S155. The terminal receives the RMSI, where the information on the PBCHincludes information about a frequency domain location for schedulinginformation of the RMSI, and the terminal may determine the frequencydomain location for the scheduling information of the RMSI based on theinformation on the PBCH, to receive the scheduling information of theRMSI based on the frequency domain location. The scheduling informationof the RMSI is used to indicate a frequency domain location at which theRMSI is located, and the terminal receives the RMSI based on thescheduling information of the RMSI.

The information on the PBCH includes resource information of a downlinkcontrol channel, and a resource of the downlink control channel is, forexample, a control resource set (CORESET). The resource information maybe frequency domain indication information, used to indicate a frequencydomain location of the CORESET. For example, the resource informationincludes CORESET offset indication information and a size of theCORESET. The CORESET offset indication information is used to indicate afrequency domain offset of the CORESET relative to a reference point.The reference point may be a lowest, central, or highest frequencydomain location of an SS (or an SS block). A value of the CORESET offsetis a frequency domain offset value of a lowest, central, or highestfrequency domain location of the CORESET relative to the referencepoint. The CORESET is used for the terminal to perform blind detectionon control information, for example, information carried on a physicaldownlink control channel (PDCCH), where the PDCCH includes common searchspace, and the common search space is used to carry public information,for example, including the scheduling information of the RMSI. Theterminal obtains a location of the CORESET, and then detects downlinkcontrol information based on the location of the CORESET to obtain thescheduling information of the RMSI; and learns, based on the schedulinginformation of the RMSI, a resource location at which the RMSI islocated, to receive the RMSI. The RMSI includes resource information ofrandom access. After the terminal receives the RMSI, a random accessprocess (S156) may start.

In the foregoing process, if the information about the frequency domainlocation for the scheduling information of the RMSI in the PBCH is aquantity of offset PRBs, and the subcarrier spacing corresponding to thePRBs is the subcarrier spacing of the SS, the lowest frequency domainlocation, implicitly obtained in this manner, of the CORESET is alignedwith a PRB grid boundary corresponding to the CORESET.

For example, in the initial access process, a subcarrier spacing of theRMSI is 30 kHz, and the subcarrier spacing of the SS is 15 kHz. When thefrequency domain location of the CORESET is indicated, a 15 kHz PRB isused as a granularity to indicate that an offset value between alocation of a center frequency of the CORESET and a location of thecenter frequency of the SS is seven PRBs, and the size of the CORESET is10 PRBs. In this case, the terminal may consider that a lowest frequencydomain location of the 10 PRBs of the CORESET is aligned with a 30 kHzPRB grid boundary.

A wideband carrier (wider BW CC, also referred to as wideband CC)concept is introduced into an NR communications system. A widebandcarrier is a carrier whose carrier bandwidth (BW) is greater than orequal to preset bandwidth, and the preset bandwidth is, for example, 100MHz. Different terminals may be allowed to access the wideband carrierby using different SSs (or SS blocks). The different SSs herein havedifferent frequency domain locations, that is, are SSs sent at differentfrequency domain locations. In other words, on a wideband carrier, thenetwork device may send a plurality of SS blocks, an SS in each SS blockmay allow one or more terminals to access the carrier, and differentterminals may access the carrier by using SSs in different SS blocks. Inthis case, when different terminals determine resources of the PBCH,grids of PRBs are not aligned with each other.

FIG. 16 is a schematic diagram of transmitting different SSs on awideband carrier according to an embodiment of this application. It isassumed that a first SS is sent at a location 161, a second SS is sentat a location 162, and the location 162 is not aligned with a boundaryof a PRB grid. Therefore, an understanding of a PRB grid by a terminalthat detects an SS at the location 162 is inconsistent with anunderstanding of a PRB grid by a terminal that detects an SS at thelocation 161. Therefore, it cannot be ensured that all terminals thatare about to access a carrier through different SSs can access thecarrier. For example, the terminal that detects the SS at the location162 cannot accurately determine a resource location of a PBCH, andaccordingly cannot access the carrier. A case shown in FIG. 17 is usedas an example for description.

FIG. 17 is a schematic diagram of accessing a same carrier by differentterminals by using different SSs according to an embodiment of thisapplication. In FIG. 17, a description is provided by using an examplein which a size of an SS raster is 100 kHz and a subcarrier spacing of aPRB is 15 kHz. A network device sends a first SS at a location 171 ofthe SS raster in FIG. 17, and sends a second SS at a location 172 of theSS raster in FIG. 17. A terminal 173 and a terminal 174 detect the SSsbased on the SS raster. The terminal 173 detects the first SS at thelocation 171 of the SS raster, and determines a PRB grid based on acenter frequency of the first SS, so as to determine a resource locationof a PBCH. The terminal 174 detects the second SS at the location 172 ofthe SS raster, and determines a PRB grid based on a center frequency ofthe second SS, so as to determine a resource location of the PBCH.However, if the PRB grid determined at the location 171 of the SS rasteris used as a reference, for the terminal 174, there may be a case of PRBgrid misalignment. As shown in FIG. 17, PRB grid boundaries determinedby the terminal 173 and the terminal 174 are not aligned with eachother. It can be learned that the terminal 173 and the terminal 174 haveinconsistent understandings of the PRB grid. Therefore, there needs tobe a terminal and a network device that have inconsistent understandingsof the PRB grid. For example, if the terminal is the terminal 174, theterminal 174 cannot correctly determine a resource location of the PBCH;therefore the terminal 174 cannot correctly receive a MIB andconsequently cannot access the carrier.

In consideration of the foregoing problem, an embodiment of thisapplication provides a communication method, so that a frequency offsetbetween center frequencies of different SSs is a positive integralmultiple of a least common multiple of a size of an SS raster and a sizeof a PRB. In this way, when determining a PRB grid based on a centerfrequency of an SS, terminals to access a same carrier by usingdifferent SSs have a consistent understanding of the PRB grid, and cancorrectly receive a MIB, so as to access the carrier. The following isdescribed with reference to the accompanying drawings.

FIG. 18 is a schematic diagram of a communication method according to anembodiment of this application. The method is used to resolve thefollowing problem: To access a same carrier by using different SSs,different terminals have inconsistent understandings of a PRB grid, andconsequently some terminals cannot access the carrier. As shown in FIG.18, the method includes the following steps.

S181. A network device sends a first SS on a carrier, where a centerfrequency of the first SS is located at a first location of an SSraster.

S182. When there is a second SS to be sent, the network device sends thesecond SS on the carrier, where a center frequency of the second SS islocated at a second location of the SS raster.

When the network device sends SSs on a same carrier, a same subcarrierspacing is used. In other words, the first SS and the second SS are sentby using the same subcarrier spacing. In addition, a frequency offsetbetween the second location and the first location is a positiveintegral multiple of a least common multiple of a size of the SS rasterand a size of a PRB, where the size of the PRB is a product of thesubcarrier spacing (collectively referred to as a subcarrier spacing ofan SS) used to send the first SS and the second SS and a quantity ofsubcarriers included in the PRB. In other words, when the second SSneeds to be sent, the network device does not directly send the secondSS at a next location of the SS raster, or does not send the second SSby randomly selecting a location of the SS raster, but sends the secondSS at the second location, where the frequency offset between the secondlocation and the first location meets a preset condition. The presetcondition is related to the size of the SS raster and the subcarrierspacing of the SS. That is, the frequency offset between the secondlocation and the first location is a positive integral multiple of aleast common multiple of the size of the SS raster and the size of thePRB, where the size of the PRB is related to the subcarrier spacing.

S183. A terminal detects an SS based on the SS raster.

When the SS is detected, the terminal achieves downlink synchronizationwith a cell based on the SS, so as to obtain system information (S184);and then initiates random access based on the system information, so asto start a random access process (S185).

In the foregoing step S181, the network device sends a first SS block,where the first SS block includes the first SS and a first PBCH, and thefirst SS includes a PSS and an SSS. In other words, the network devicesends the first SS and broadcasts information on the first PBCH. Infrequency domain, the center frequency of the first SS and a centerfrequency of the first PBCH are located at the first location of the SSraster. In time domain, the network device may periodically send thefirst SS at the first location and broadcast the information on thefirst PBCH.

In the foregoing step S182, the network device sends a second SS block,where the second SS block includes the second SS and a second PBCH, andthe second SS includes a PSS and an SSS. In other words, the networkdevice sends the second SS and broadcasts information on the secondPBCH. The PSS/SSS of the first SS and the PSS/SSS of the second SS maybe a same SS sequence, but have different frequency domain locations. Infrequency domain, the center frequency of the second SS and a centerfrequency of the second PBCH are located at the second location of theSS raster. In time domain, the network device may periodically send thesecond SS at the second location and broadcast the information on thesecond PBCH.

When there are a plurality of SSs on a carrier for terminals to accessthe carrier, to enable PRB grids determined by different terminals basedon different SSs to be aligned with each other, that is, to enable theterminals to have a consistent understanding of the PRB grids, in theforegoing embodiment, a frequency offset between center frequencies ofdifferent SSs (namely, the frequency offset between the second locationand the first location) is limited to a positive integral multiple of aleast common multiple of a size of an SS raster and a size of a PRB. Thefollowing is described by using examples of different sizes of the SSraster and different sizes of the subcarrier spacing.

FIG. 19 is a schematic diagram of accessing a same carrier by differentterminals by using different SSs according to an embodiment of thisapplication. Assuming that a size of an SS raster is 100 kHz and asubcarrier spacing of an SS is 15 kHz, a size of a PRB is 15*12 kHz,namely, 180 kHz. A least common multiple of 100 and 180 is 900, and afrequency offset between center frequencies (or locations of an SSraster at which SSs are located) of different SSs in a carrier is 900*nkHz, where n is a positive integer. In this case, a terminal 193 thatdetects an SS from a first location 191 of the SS raster and a terminal194 that detects an SS from a second location 192 of the SS raster havea consistent understanding of PRB grids. Therefore, the terminal 93 andthe terminal 194 both can correctly receive a MIB, so as to access thecarrier.

Assuming that a size of an SS raster is 100 kHz and a subcarrier spacingof an SS is 30 kHz, a size of a PRB is 30*12 kHz, namely, 360 kHz. Aleast common multiple of 100 and 180 is 1800, and a frequency offsetbetween center frequencies (or locations of an SS raster at which SSsare located) of different SSs in a carrier is 1800*n kHz, where n is apositive integer.

Assuming that a size of an SS raster is 180 kHz and a subcarrier spacingof an SS is 15 kHz, a size of a PRB is 15*12 kHz, namely, 180 kHz. Afrequency offset between center frequencies (or locations of an SSraster at which SSs are located) of different SSs in a carrier is 180*nkHz, where n is a positive integer. In this case, the size of the PRB isthe same as the size of the SS raster. Therefore, a least commonmultiple is 180 kHz. It may also be understood that there is no need tolimit the frequency offset between the center frequencies of differentSSs, and the network device can send the SS at any two locations of theSS raster. When a size of an SS raster is 180 kHz, assuming that asubcarrier spacing of an SS is 30 kHz, a size of a PRB is 30*12 kHz,namely, 360 kHz. A least common multiple of 180 and 360 is 360, and afrequency offset between center frequencies (or locations of an SSraster at which SSs are located) of different SSs in a carrier is 360*nkHz, where n is a positive integer.

Assuming that a size of an SS raster is 720 kHz and a subcarrier spacingof an SS is 120 kHz, a size of a PRB is 120*12 kHz, namely, 1440 kHz. Aleast common multiple of 720 and 1440 is 1440, and a frequency offsetbetween center frequencies (or locations of an SS raster at which SSsare located) of different SSs in a carrier is 1440*n kHz, where n is apositive integer. When a size of an SS raster is 720 kHz, assuming thata subcarrier spacing of an SS is 240 kHz, a size of a PRB is 240*12 kHz,namely, 2880 kHz. A least common multiple of 720 and 2880 is 2880, and afrequency offset between center frequencies (or locations of an SSraster at which SSs are located) of different SSs in a carrier is 2880*nkHz, where n is a positive integer.

The foregoing gives a plurality of examples of sizes of the SS rasterand sizes of the subcarrier spacing, and describes conditions to be metby a frequency offset between center frequencies of different SSs in acase of corresponding sizes. These examples are merely for ease ofunderstanding this embodiment and are not intended to limit thisapplication. A person skilled in the art may implement, based on theforegoing embodiment, SS sending with various combinations of the SSraster and the subcarrier spacing.

In the foregoing step S183, some terminals may detect an SS at the firstlocation, and some terminals may detect an SS at the second location. Itis assumed that a terminal that detects an SS at the first location is afirst terminal, where there may be one or more first terminals; and itis assumed that a terminal that detects an SS at the second location isa second terminal, where there may be one or more second terminals.

In the foregoing step S184, the system information obtained by theterminal may include a MIB and RMSI. When the terminal is the firstterminal, the first terminal detects the first SS at the first locationof the SS raster, and determines a resource location of the first PBCHbased on the first SS, for example, 24 PRBs that center on the centerfrequency of the first SS; and then receives, on the first PBCH, a firstMIB sent by the network device. When the terminal is the secondterminal, the second terminal detects the second SS at the secondlocation of the SS raster, and determines a resource location of thesecond PBCH based on the second SS, for example, 24 PRBs that center onthe center frequency of the second SS; and then receives, on the secondPBCH, a second MIB sent by the network device.

Any one of the foregoing MIBs may include resource information, wherethe resource information is used to indicate a resource location of acontrol channel at which RMSI scheduling information is located. Afterthe terminal correctly parses a MIB, the terminal receives, based onresource information in the MIB, RMSI scheduling information sent by thenetwork device, then receives RMSI based on the RMSI schedulinginformation, and initiates random access based on the RMSI, so as toaccess the carrier.

In an implementation, resource information of a downlink control channelis carried on a PBCH, and a resource of the downlink control channel is,for example, a control resource set (CORESET). The resource informationmay be frequency domain indication information, used to indicate afrequency domain location of the CORESET. Optionally, the resourceinformation includes a CORESET offset value and a size of the CORESET.The CORESET offset value is used to indicate a frequency offset of theCORESET relative to a reference point. The reference point may be alowest, central, or highest frequency domain location of an SS (or an SSblock). The CORESET offset value is a frequency offset of a lowest,central, or highest frequency domain location of the CORESET relative tothe reference point. The CORESET is used for the terminal to performblind detection on control information, for example, information carriedon a physical downlink control channel (PDCCH), where the PDCCH includescommon search space, and the common search space is used to carry publicinformation, for example, including the scheduling information of theRMSI. The terminal obtains a location of the CORESET based on the MIB,and then detects downlink control information based on the location ofthe CORESET to obtain the scheduling information of the RMSI; and learnsof, based on the scheduling information of the RMSI, a resource locationat which the RMSI is located, to receive the RMSI. After the terminalreceives the RMSI, a random access process may start.

For example, the first terminal determines, based on first resourceinformation in the first MIB, a resource location of a control channelat which first RMSI scheduling information is located. Then the firstterminal receives the first RMSI scheduling information on the controlchannel, determines a resource location at which first RMSI is locatedbased on the first RMSI scheduling information, and receives the firstRMSI at the determined resource location. Likewise, the second terminaldetermines, based on second resource information in the second MIB, aresource location of a control channel at which second RMSI schedulinginformation is located. Then the second terminal receives the secondRMSI scheduling information on the control channel, determines aresource location at which second RMSI is located based on the secondRMSI scheduling information, and receives the second RMSI at thedetermined resource location.

It can be learned that when a terminal accesses a carrier, first an SSis blindly detected, a frequency domain location of a PBCH is determinedbased on the detected SS, and then a MIB carried on the PBCH is receivedat the determined frequency domain location. The MIB includesinformation about a CORESET that is used to transmit downlink controlinformation. The terminal determines a frequency domain location of theCORESET based on the information, and then receives control informationcarried on the PDCCH at the determined frequency domain location. Thecontrol information includes scheduling information of RMSI, and theterminal determines a frequency domain location, of the RMSI, on aphysical downlink shared channel (PDSCH) based on the schedulinginformation of the RMSI. Further, the terminal can receive the RMSI atthe determined frequency domain location. The RMSI may carry randomaccess information, and the terminal may initiate random access based onthe RMSI.

In the foregoing embodiments, the size of the SS raster and thesubcarrier spacing of the SS determine the frequency offset between thecenter frequencies of different SSs; or, in other words, the size of theSS raster and the subcarrier spacing of the SS determine a frequencyoffset between locations of an SS raster at which different SSs aresent. In another implementation provided in this embodiment of thisapplication, the size of the SS raster and the subcarrier spacing of theSS are determined according to a carrier frequency, and the size of theSS raster is a positive integral multiple of a size of a PRBcorresponding to the subcarrier spacing of the SS. In this way,regardless of the SS raster locations at which different SSs are sent,terminals that detect the different SSs have a consistent understandingof a PRB grid. Therefore, terminals to access a same carrier by usingthe different SSs can correctly receive system information and accessthe carrier without using the foregoing frequency domain locationrestriction manner.

FIG. 20 is a schematic diagram of another communication method accordingto an embodiment of this application. The method is used to resolve thefollowing problem: To access a same carrier by using different SSs,different terminals have inconsistent understandings of a PRB grid, andconsequently some terminals cannot access the carrier. As shown in FIG.20, the method includes the following steps:

S201. A network device determines a size of an SS raster and asubcarrier spacing of an SS based on a frequency of a carrier.

S202. The network device sends an SS on the carrier by using thedetermined subcarrier spacing, where a center frequency of the SS is ata location of the SS raster, and a distance between two adjacentlocations of the SS raster is the determined size of the SS raster.

Correspondingly, FIG. 21 is a schematic diagram of another communicationmethod according to an embodiment of this application. The method isused to resolve the following problem: To access a same carrier by usingdifferent SSs, different terminals have inconsistent understandings of aPRB grid, and consequently some terminals cannot access the carrier. Asshown in FIG. 21, the method includes the following steps:

S211. A terminal determines a size of an SS raster and a subcarrierspacing of an SS based on a frequency of a carrier, where the size ofthe SS raster is a positive integral multiple of a size of a PRB, andthe size of the PRB is a product of the subcarrier spacing of the SS anda quantity of subcarriers included in the PRB.

S212. The terminal detects an SS on the carrier based on the SS rasterby using the subcarrier spacing of the SS, where a distance between twoadjacent locations of the SS raster is the determined size of the SSraster, and a center frequency of the SS is at a location of the SSraster.

Optionally, in the foregoing embodiment, the size of the SS raster isequal to the size of the PRB corresponding to the subcarrier spacing ofthe SS. For example, Table 2 below shows sizes of the subcarrier spacingof the SS and sizes of the SS raster at several carrier frequencies.Regardless of SS raster locations at which different SSs are sent,terminals that detect the different SSs have a consistent understandingof a PRB grid. Therefore, terminals to access a same carrier by usingthe different SSs can correctly receive system information and accessthe carrier without using the foregoing frequency domain locationrestriction manner.

TABLE 2 Subcarrier spacing Carrier frequency f of an SS SS raster f < 3GHz 15 kHz 180 kHz 3 GHz < f < 6 GHz 30 kHz 360 kHz

The embodiments shown in FIG. 18, FIG. 20, and FIG. 21 may be combinedwith the foregoing embodiment. To be specific, when sending of differentSSs is supported on a carrier, the foregoing method may be used, so thatterminals to access the carrier by using different SSs can have aconsistent understanding of a PRB grid. In addition, by using the methodin the foregoing embodiment, a terminal can correctly obtain a PRB gridused to perform data/control information transmission, so as tocorrectly perform data/control information transmission and reception.

An embodiment of this application further provides an apparatusconfigured to implement any one of the foregoing methods, for example,provides an apparatus that includes units (or means) configured toimplement the steps performed by the terminal in any one of theforegoing methods; and for another example, further provides anotherapparatus that includes units (or means) configured to implement thesteps performed by the network device in any one of the foregoingmethods.

It should be understood that the division of the units in the apparatusis merely division of logical functions. During actual implementation,all or some of the units may be integrated into a physical entity, ormay be physically separated. In addition, all the units in the apparatusmay be implemented in a form of software invoked by a processingelement, or may be implemented by hardware; or some units may beimplemented in a form of software invoked by a processing element, andsome units may be implemented by hardware. For example, duringimplementation, a unit may be a separately disposed processing element,or may be integrated into a chip of the apparatus. Alternatively, theunit may be stored in a form of a program in a memory and invoked by aprocessing element of the apparatus to perform a function of the unit.Implementation of other units is similar thereto. In addition, all orsome of these units may be integrated or separately implemented. Theprocessing element herein may be an integrated circuit having a signalprocessing capability. During an implementation process, the steps ofthe foregoing methods or the foregoing units may be completed by using ahardware-integrated logic circuit in a processor element or instructionsin a form of software.

For example, the units in the apparatus may be configured as one or moreintegrated circuits for implementing the foregoing methods, for example,one or more application-specific integrated circuits (ASIC), one or moredigital signal processors (DSP), one or more field programmable gatearrays (FPGA), or the like. For another example, when the units in theapparatus may be implemented in a form of scheduling a program by aprocessing element, the processing element may be a general purposeprocessor, for example, a central processing unit (CPU) or anotherprocessor that can invoke a program. For another example, these unitsmay be integrated together, and implemented in a system-on-a-chip (SOC)form.

FIG. 22 is a schematic structural diagram of a network device accordingto an embodiment of this application, to implement operations of thenetwork device in the foregoing embodiments. As shown in FIG. 22, thenetwork device includes: an antenna 221, a radio frequency apparatus222, and a baseband apparatus 223. The antenna 221 is connected to theradio frequency apparatus 221. In an uplink direction, the radiofrequency apparatus 222 receives, through the antenna 221, informationsent by a terminal, and sends the information sent by the terminal tothe baseband apparatus 223 for processing. In a downlink direction, thebaseband apparatus 223 processes information for the terminal, and sendsthe information for the terminal to the radio frequency apparatus 222,and the radio frequency apparatus 222 processes the information for theterminal, and then sends the processed information to the terminalthrough the antenna 221.

The foregoing apparatus applied to the network device may be located inthe baseband apparatus 223. In an implementation, the units throughwhich the network device implements the steps in the foregoing methodsmay be implemented in a form of scheduling a program by a processingelement. For example, the baseband apparatus 223 includes a processingelement 2231 and a storage element 2232. The processing element 2231invokes a program stored in the storage element 2232, to perform themethods performed by the network device in the foregoing methodembodiments. In addition, the baseband apparatus 223 may further includean interface 2233, configured to exchange information with the radiofrequency apparatus 222. The interface is, for example, a common publicradio interface (CPRI).

In another implementation, the units through which the network deviceimplements the steps in the foregoing methods may be configured as oneor more processing elements. These processing elements are disposed onthe baseband apparatus 223. The processing elements herein may be anintegrated circuit, for example, one or more ASICs, one or more DSPs,one or more FPGAs, or the like. These integrated circuits may beintegrated to form a chip.

These units may be integrated together, and implemented in asystem-on-a-chip (SOC) form. For example, the baseband apparatus 223includes an SOC chip, configured to implement the foregoing methods. Thechip may be integrated with the processing element 2231 and the storageelement 2232, and the processing element 2231 invokes the program storedin the storage element 2232 to implement the foregoing methods performedby the network device; or the chip may be integrated with at least oneintegrated circuit, to implement the foregoing methods performed by thenetwork device; or the foregoing implementations may be combined, wherefunctions of some units are implemented by the processing element byinvoking a program, and functions of some units are implemented by anintegrated circuit.

Regardless of a used manner, the foregoing apparatus applied to thenetwork device includes at least one processing element and a storageelement, where the at least one processing element is configured toperform the methods that are performed by the network device and thatare provided in the foregoing method embodiments. The processing elementmay perform, in a first manner, that is, by invoking a program stored inthe storage element, some or all of the steps performed by the networkdevice in the foregoing method embodiments; or may perform, in a secondmanner, that is, by using a hardware-integrated logic circuit in aprocessor element and instructions, some or all of the steps performedby the network device in the foregoing method embodiments; or certainly,may perform, by combining the first manner and the second manner, someor all of the steps performed by the network device in the foregoingmethod embodiments.

The processing element herein is the same as that in the foregoingdescription, and may be a general purpose processor, for example, acentral processing unit (CPU), or may be configured as one or moreintegrated circuits for implementing the foregoing methods, for example,one or more application-specific integrated circuits (ASIC), one or moredigital signal processors (DSP), one or more field programmable gatearrays (FPGA), or the like.

The storage element may be a memory, or may be a collective name for aplurality of storage elements.

FIG. 23 is a schematic structural diagram of a terminal according to anembodiment of this application. The terminal may be the terminal in theforegoing embodiments, configured to implement operations of theterminal in the foregoing embodiments. As shown in FIG. 23, the terminalincludes: an antenna, a radio frequency apparatus 231, and a basebandapparatus 232. The antenna is connected to the radio frequency apparatus231. In a downlink direction, the radio frequency apparatus 231receives, through the antenna, information sent by a network device, andsends the information sent by the network device to the basebandapparatus 232 for processing. In an uplink direction, the basebandapparatus 232 processes information from the terminal, and sends theinformation from the terminal to the radio frequency apparatus 231, andthe radio frequency apparatus 231 processes the information from theterminal, and then sends the processed information to the network devicethrough the antenna.

The baseband apparatus may include a modem subsystem, configured toprocess data at various communications protocol layers; may furtherinclude a central processing subsystem, configured to process a terminaloperating system and an application layer; and may further include othersubsystems, such as a multimedia subsystem and a peripheral subsystem,where the multimedia subsystem is configured to control a camera, screendisplay, and the like of the terminal, and the peripheral subsystem isconfigured to implement connection with another device. The modemsubsystem may be a separately disposed chip. Optionally, a processingapparatus of the foregoing frequency domain resource may be implementedon the modem subsystem.

In an implementation, the units through which the terminal implementsthe steps in the foregoing methods may be implemented in a form ofscheduling a program by a processing element. For example, a subsystemof the baseband apparatus 232, such as a modem subsystem, includes aprocessing element 2321 and a storage element 2322. The processingelement 2321 invokes a program stored in the storage element 2322, toperform the methods performed by the terminal in the foregoing methodembodiments. In addition, the baseband apparatus 232 may further includean interface 2323, configured to exchange information with the radiofrequency apparatus 231.

In another implementation, the units through which the terminalimplements the steps in the foregoing methods may be configured as oneor more processing elements. These processing elements are disposed on aparticular subsystem of the baseband apparatus 232, for example, a modemsubsystem. The processing elements herein may be an integrated circuit,for example, one or more ASICs, one or more DSPs, one or more FPGAs, orthe like. These integrated circuits may be integrated to form a chip.

For example, the units through which the terminal implements the stepsin the foregoing methods may be integrated together, and implemented ina system-on-a-chip (SOC) form. For example, the baseband apparatus 232includes an SOC chip, configured to implement the foregoing methods. Thechip may be integrated with the processing element 2321 and the storageelement 2322, and the processing element 2321 invokes the program storedin the storage element 2322 to implement the foregoing methods performedby the terminal; or the chip may be integrated with at least oneintegrated circuit, to implement the foregoing methods performed by theterminal; or the foregoing implementations may be combined, wherefunctions of some units are implemented by the processing element byinvoking a program, and functions of some units are implemented by anintegrated circuit.

Regardless of a used manner, the foregoing apparatus applied to theterminal includes at least one processing element and a storage element,where the at least one processing element is configured to perform themethods that are performed by the terminal and that are provided in theforegoing method embodiments. The processing element may perform, in afirst manner, that is, by scheduling a program stored in the storageelement, some or all of the steps performed by the terminal in theforegoing method embodiments; or may perform, in a second manner, thatis, by using a hardware-integrated logic circuit in a processor elementand instructions, some or all of the steps performed by the terminal inthe foregoing method embodiments; or certainly, may perform, bycombining the first manner and the second manner, some or all of thesteps performed by the terminal in the foregoing method embodiments.

The processing element herein is the same as that in the foregoingdescription, and may be a general purpose processor, for example, acentral processing unit (CPU), or may be configured as one or moreintegrated circuits for implementing the foregoing methods, for example,one or more application-specific integrated circuits (ASIC), one or moredigital signal processors (DSP), one or more field programmable gatearrays (FPGA), or the like.

The storage element may be a memory, or may be a collective name for aplurality of storage elements.

A person of ordinary skill in the art may understand that all or some ofthe steps in the method embodiments may be implemented by a programinstructing related hardware. The program may be stored in a computerreadable storage medium. When the program runs, the steps in the methodembodiments are performed. The foregoing storage medium includes: anymedium that can store program code, such as a ROM, a RAM, a magneticdisk, or an optical disc.

What is claimed is:
 1. A communication method, comprising: receiving, bya terminal, a synchronization signal from a network device, wherein aphysical resource block grid used for the synchronization signal is afirst physical resource block grid; receiving, by the terminal, firstindication information from the network device, wherein the firstindication information is used to indicate a first frequency offsetbetween the first physical resource block grid and a second physicalresource block grid; determining, by the terminal, the second physicalresource block grid based on the first physical resource block grid andthe first frequency offset; and receiving, by the terminal, secondindication information from the network device, wherein the secondindication information is used to indicate a second frequency offsetbetween the second physical resource block grid and a third physicalresource block grid.
 2. The method according to claim 1, furthercomprising: determining, by the terminal, the first physical resourceblock grid based on the synchronization signal.
 3. The method accordingto claim 1, further comprising: determining, by the terminal, the thirdphysical resource block grid based on the second physical resource blockgrid and the second frequency offset.
 4. The method according to claim1, further comprising: performing, by the terminal, informationtransmission with the network device based on the third physicalresource block grid.
 5. The method according to claim 1, wherein thereceiving the first indication information comprises: receiving, by theterminal, the first indication information through a physical broadcastchannel (PBCH).
 6. The method according to claim 1, wherein thereceiving the second indication information comprises: receiving, by theterminal, remaining minimum system information (RMSI), wherein the RMSIcarries the second indication information.
 7. The method according toclaim 1, wherein a subcarrier spacing of the second physical resourceblock grid is 15 kHz or 60 kHz.
 8. The method according to claim 1,wherein a subcarrier spacing of the second physical resource block gridis the same as a subcarrier spacing of the synchronization signal. 9.The method according to claim 1, wherein a subcarrier spacing of thethird physical resource block grid is greater than the subcarrierspacing of the second physical resource block grid.
 10. A communicationsapparatus, comprising a processor configured to connect with anon-transitory computer readable storage medium, wherein thenon-transitory computer readable storage medium stores a program, andwhen the program is executed by the processor, the following steps areperformed: receiving a synchronization signal from a network device,wherein a physical resource block grid used for the synchronizationsignal is a first physical resource block grid; receiving firstindication information from the network device, wherein the firstindication information is used to indicate a first frequency offsetbetween the first physical resource block grid and a second physicalresource block grid; determining the second physical resource block gridbased on the first physical resource block grid and the first frequencyoffset; and receiving second indication information from the networkdevice, wherein the second indication information is used to indicate asecond frequency offset between the second physical resource block gridand a third physical resource block grid.
 11. The apparatus according toclaim 10, wherein when the program is executed by the processor, thefollowing step is further performed: determining the first physicalresource block grid based on the synchronization signal.
 12. Theapparatus according to claim 10, wherein when the program is executed bythe processor, the following step is further performed: determining thethird physical resource block grid based on the second physical resourceblock grid and the second frequency offset.
 13. The apparatus accordingto claim 10, wherein when the program is executed by the processor, thefollowing step is further performed: performing information transmissionwith the network device based on the third physical resource block grid.14. The apparatus according to claim 10, wherein the first indicationinformation is received through a physical broadcast channel (PBCH). 15.The apparatus according to claim 10, wherein the second indicationinformation is received through remaining minimum system information(RMSI).
 16. The apparatus according to claim 10, wherein a subcarrierspacing of the second physical resource block grid is 15 kHz or 60 kHz.17. The apparatus according to claim 10, wherein a subcarrier spacing ofthe second physical resource block grid is the same as a subcarrierspacing of the synchronization signal.
 18. The apparatus according toclaim 10, wherein a subcarrier spacing of the third physical resourceblock grid is greater than the subcarrier spacing of the second physicalresource block grid.
 19. A communications apparatus, comprising atransceiver and a processor, wherein: the transceiver is configured toreceive a synchronization signal from a network device, wherein aphysical resource block grid used for the synchronization signal is afirst physical resource block grid; the transceiver is furtherconfigured to receive first indication information from the networkdevice, wherein the first indication information is used to indicate afirst frequency offset between the first physical resource block gridand a second physical resource block grid; the processor is configuredto determine the second physical resource block grid based on the firstphysical resource block grid and the first frequency offset; and thetransceiver is further configured to receive second indicationinformation from the network device, wherein the second indicationinformation is used to indicate a second frequency offset between thesecond physical resource block grid and a third physical resource blockgrid.
 20. The apparatus according to claim 19, wherein the processor isfurther configured to: determine the first physical resource block gridbased on the synchronization signal.
 21. The apparatus according toclaim 19, wherein the processor is further configured to: determine thethird physical resource block grid based on the second physical resourceblock grid and the second frequency offset.
 22. The apparatus accordingto claim 19, wherein the transceiver is further configured to: performinformation transmission with the network device based on the thirdphysical resource block grid.
 23. The apparatus according to claim 19,wherein the first indication information is received through a physicalbroadcast channel (PBCH).
 24. The apparatus according to claim 19,wherein the second indication information is received through remainingminimum system information (RMSI).
 25. The apparatus according to claim19, wherein a subcarrier spacing of the second physical resource blockgrid is 15 kHz or 60 kHz.
 26. The apparatus according to claim 19,wherein a subcarrier spacing of the second physical resource block gridis the same as a subcarrier spacing of the synchronization signal. 27.The apparatus according to claim 19, wherein a subcarrier spacing of thethird physical resource block grid is greater than the subcarrierspacing of the second physical resource block grid.
 28. A non-transitorycomputer-readable storage medium, comprising a program, wherein whenbeing executed by a processor, the following steps are performed:receiving a synchronization signal from a network device, wherein aphysical resource block grid used for the synchronization signal is afirst physical resource block grid; receiving first indicationinformation from the network device, wherein the first indicationinformation is used to indicate a first frequency offset between thefirst physical resource block grid and a second physical resource blockgrid; determining the second physical resource block grid based on thefirst physical resource block grid and the first frequency offset; andreceiving second indication information from the network device, whereinthe second indication information is used to indicate a second frequencyoffset between the second physical resource block grid and a thirdphysical resource block grid.
 29. The non-transitory computer-readablestorage medium according to claim 28, wherein when the program isexecuted by the processor, the following step is further performed:determining the first physical resource block grid based on thesynchronization signal.
 30. The non-transitory computer-readable storagemedium according to claim 28, wherein when the program is executed bythe processor, the following step is further performed: determining thethird physical resource block grid based on the second physical resourceblock grid and the second frequency offset.